A used-car dealer is purchasing 50 used BMWs from one dealer in order to sell them for a profit. Working with collected data, the dealer has found a regression model to predict the selling price on the basis of the car’s age. He wants to predict the total amount he will get for these 50 cars in order to make sure he does not lose money. All 50 cars are three years old (they were turned in after their leases expired). Should he use a confidence interval or a prediction interval for the mean selling price of these 50 cars? Explain.