A shoe store developed the following estimated regression equation relating sales to inventory investment and advertising expenditures. y = 21 + 10x,+ 6X2 where X1 = inventory investment ($1,000s) X, = advertising expenditures ($1,000s) y = sales ($1,000s). (a) Predict the sales (in dollars) resulting from a $15,000 investment in inventory and an advertising budget of $10,000. (b) Interpret b, and b, in this estimated regression equation. Sales can be expected to increase by $ for every dollar increase in inventory investment when advertising expenditure is held constant. Sales can be expected to increase by for every dollar increase in advertising expenditure when inventory investment is held constant