Question

Suppose that a household's monthly water bill (in dollars) is a linear function of the amount of water the household uses (in hundreds of cubic feet, HCF). When graphed, the function gives a line with a slope of 1.35 . See the figure below.

If the monthly cost for13 HCF is 25.43$ , what is the monthly cost for 19 HCF?

Answer 1

Given:
y = mx + b

m = slope
b = y-intercept.

m = 1.35

x = 13

25.43 = 1.35(13) + b
25.43 = 17.55 + b
b = 25.43 - 17.55
b = 7.88

y = 1.35(19) + 7.88
y = 25.65 + 7.88
y = 33.53

The monthly cost for 19HCF is $33.53