The gas tank of a certain car contains 13 gal when the driver of the car begins a trip. For each mile driven by the driver, the amount of gas in the tank decreases by 0.025 gal.

a. Write a linear function for the number of gallons of gas in the tank in terms of the number of miles driven.

b. Use your equation to find the number of gallons in the tank after 180 miles are driven.