Getting Started 
Misconception/Error The student is unable to correctly write an expression that represents the monthly cost of water. 
Examples of Student Work at this Level The student:
 Writes an equation in one variable such as 6.53x = 32 or 32 + 6.53x = 1000.
 Writes an equation that does not contain the defined variableÂ x such as 32 + 6.53 = c.
 Writes an expression such as 6.53 + 32x orÂ 6.53x + 32x.

Questions Eliciting Thinking Can you explain in your own words how the monthly water bill is determined?
What is the unknown in this problem?
How many times will you pay the $32 in one month?
How many times will you have to pay the $6.53?
What is a function? What does function notation look like? 
Instructional Implications Review the concept of a function and what it means to write a function. Provide examples of functions written from verbal descriptions with a focus on linear relationships.
Review the concept of a linear function in twovariables emphasizing slopeintercept form. Be sure the student understands the specific role of the rate of change (or slope) and the initial value (or yintercept) in determining functional values. Guide the student through additional examples of verbal descriptions of linear functions and ask the student to identify the rate of change and the initial value and then, write a function in slopeintercept form. Ask the student to use the function to calculate functional values given specific values of the independent variable.
Ask the student to create a table of values and calculate the cost when the usage is 0, 1, 2, and 3 kilogallons per month. Ask the student to write out each calculation [e.g., 6.53(0) + 32]. Guide the student to use the form of the calculations to write an expression for the cost of water for oneÂ month. Then, assist the student in using this expression to write the equation. 
Moving Forward 
Misconception/Error The student writes an expression rather than a function. 
Examples of Student Work at this Level The student writes 32 + 6.53x or 6.53x + 32.

Questions Eliciting Thinking What is the difference between an expression and a function?
What does the expression you wrote represent? What is missing from your function? 
Instructional Implications Review the concept of a linear function in twovariables emphasizing slopeintercept form. Be sure the student understands the role of each variable. If needed, review function notation. Assist the student in revising his or her answer, so it is written as a function. Ask the student to explicitly define each variable. Provide additional opportunities to write functions from verbal descriptions. 
Almost There 
Misconception/Error The student provides a correct response but with an insufficientÂ explanation. 
Examples of Student Work at this Level The student correctly writes the function as f(x) = 6.53x + 32 or y = 6.53x + 32 but is unable to correctly explain or justify his or her work. The student provides no explanation or an incomplete one.Â For example, the student says:
 The m has to be the one that keeps changing and b has to be the one that does not change.
 The $6.53 goes first because that is the slope, and the $32 is the yintercept.

Questions Eliciting Thinking Can you explain in your own words how the monthly water bill is determined?
Can you explain why you wrote your function the way that you did? How is your function related to the context of the problem?
What does x represent in this problem? What does f(x) represent? How can you describe the relationship between x and f(x). 
Instructional Implications Assist the student in relating the function written to the given verbal description. Ask the student to explain both terms (i.e., 6.53x and 32) in the context of the problem. Provide assistance as needed. Provide additional opportunities to write functions from verbal descriptions. 
Got It 
Misconception/Error The student provides complete and correct responses to all components of the task. 
Examples of Student Work at this Level The student writes the function as f(x) = 6.53x + 32. The student explains that f(x) is the total monthly charge when x kilogallons of water are used. The total monthly bill is found by multiplying the number of kilogallons of water used by $6.53 and then adding the base fee of $32.

Questions Eliciting Thinking How can you use function notation to represent the dependent variable? What does this notation mean?
Can you describe what the graph of this function would look like?
Are there any restrictions on the domain of this function? Are there any restrictions on the range of this function? 
Instructional Implications Ask the student to write linear and exponential functions from verbal descriptions and to analyze the features of the descriptions that indicate which type of function is most appropriate. Encourage the student to use function notation.
Ask the student to write a function given a table of values or a graph. Consider using the MFAS tasks Writing a Function From Ordered Pairs (FLE.1.2), What Is the Function Rule?Â (FLE.1.2) and Functions From Graphs (FLE.1.2) if not used previously. 