A candy bar manufacturer is interested in trying to estimate how sales are ...

A candy bar manufacturer is interested in trying to estimate how sales are influenced by the price of their product.  To do this, the company randomly chooses 6 small cities and offers the candy bar at different prices.  Using candy bar sales as the dependent variable, the company will conduct a simple linear regression on the data below:
 

City       Price ($) Sales
River Falls 1.3 100
Hudson         1.6 90
Ellisworth 1.8 90
Prescott 2 40
Rock Elm 2.4 38
Stillwater 2.9 32
 

a. What is the estimated average change in the sales of the candy bar if price goes up $1.00?
 

b. What percent of the total variation in candy bar sales is explained by prices?