Question

The monthly cost (in dollars) of water use is a linear function of the amount of water used (in hundreds of cubic feet, HCF). The cost for using 20 HCF of water is$35.79, and the cost for using 32 HCF is $51.99. What is the cost for using 29 HCF of water?

Answer 1

20 cm3 = $35.79

32 cm3 = $51.99

29 cm3 = ?

slope = (51.99 - 35.79) / (32 - 20)

slope = 16.2/12

slope = 1.35

Equation of the line

y - 35.79 = 1.35(x - 20)

Solve for y

y = 1.35x - 27 + 35.79

y = 1.35x + 8.79

Find the cost of 29 cm3

y = 1.35(29) + 8.79

y = 39.15 + 8.79

y = $47.94