Which of these statements is true for f(x)=(1/10)^x

Suppose that a households 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 slope of 1.65. if the monthly cost for 13 hcf is $46.10 what is the monthly cost for 19 hcf?

How long must $542 be invested at a rate of 7% to earn $303.52 in interest? in a easier way

Extra points! find the missing dimension! need asap