the following regression model has been proposed to predict sales at a computer store. y = 50 - 3x1 + 20x2 + 10x3 where x1 = competitor's previous day's sales (in $1000s), x2 = population within 1 mile (in 1,000s) x3 1.) if radio advertising was used 2.) if otherwise y = sales (in $1000s). predict sales (in dollars) for a store with the competitor's previous day's sale of $5000, a population of 20,000 within i mile , and nine radio advertisements