The total cost of four pens and seven mechanical pencils is $13.25. The cost of each pencil is 75 cents.
a. Using an arithmetic approach, find the cost of a pen.
b. Let the cost of a pen be dollars. Write an expression for the total cost of four pens and seven mechanical pencils in terms of .
c. Write an equation that could be used to find the cost of a pen.
d. Determine a value for for which the equation you wrote in part (b) is true.