Sales are often related to economic indicators. One possible indicator is the unemployment rate. Data for a large retail store were used to obtain a linear regression model to predict quarterly Sales ($ billion) based on unemployment Rate (in %) over a period of four years. This regression model produced an R² = 88.3, and a slope of -2.99. 

a) Interpret the meaning of R².

b) What is the correlation of Sales and unemployment Rate?

c) If a quarter has an unemployment Rate 1% larger than another, what is the predicted impact on Sales?