cant fogure this out

A shoe store developed the following estimated regression equation relating sales to inventory Investment and advertising expenditures. y = 30 +961 +622 where 21 =inventory investment ($1000) 12 = advertising expenditures ($1000s) y = sales ($1000s) a. Predict the sales resulting from a $15,000 investment in inventory and an advertising budget of $10,000 $ b. Interpret b1 and by in this estimated regression equation. bi: Sales can be expected to select your answer. y by $9 for every dollar increase in Select your answer held constant. by: Sales can be expected to - Select your answer by $6 for every dollar increase in Select your answer - held constant when Select your answer - vis when - Select your answer - is