Management proposed the following regression model to predict sales at a fast-food outlet. y=0+1x1+2x2+3x3+ where x1= number of competitors within one mile x2= population within one mile (1000s) x3={10ifdrive-upwindowpresentotherwise y= sales ($1000s) The following estimated regression equation was developed after 20 outlets were surveyed. y^=10.54.9x1+6.2x2+15.6x3 a. What is the expected amount of sales attributable to the drive-up window? $ b. Predict sales for a store with two competitors, a population of 9,000 within one mile, and no drive-up window. Estimate of sales =$ c. Predict sales for a store with one competitor, a population of 4,000 within 1 mile, and a drive-up window. Estimate of sales =$