linear equation

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 1.65

If the monthly cost for 12 HCF is $49.47,what is the monthly cost for 8 HCF

Answer 1

Let y-axis represent cost and x-axis represent amount of water use in HCF

The equation of line passing through point (12, 49.47) and slope 1.65 is

y – 49.47 = 1.65 ( x – 12)

To find cost y for x = 8 HCF substitute x = 8 in above equation

 y – 49.47 = 1.65 (8 – 12) solve for y

y = 49.47 – 1.65*4 = 49.47 – 6.6 = $42.87