Does anyone know how to answer question 7?

Suppose a pendulum is l meters long. the time, t,in seconds that it tales to swing back and forth once is given by t=2.01

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?

A50% increase followed by 33 1/2% decrease