Sally has been running the following number of ads in the local newspaper to help attract customers into her store. She has also been keeping track of customers who have come into the store as a result of the ads, as well as the amount of money they spend.This is the data from the last 4 weeks:

Numbers of Ads	Increased Sales
16	330
12	270
18	380
14	300

a) Determine the equation that relates ads and increased sale (8 marks)

b) If Sally runs 15 ads, how much will sales increase? (3 marks)