The price of a portrait during Month 21

Let Yt be the sales during month t (in thousands of dollars) for a photography studio, and let Pt be the price charged for portraits during month t. The data are in the file Week 4 Assignment Chapter 12 Problem 64 Download Week 4 Assignment Chapter 12 Problem 64. Use regression to fit the following model to these data: Yt = a + b1Yt−1 + b2Pt + et This equation indicates that last month’s sales and the current month’s price are explanatory variables. The last term, et, is an error term. complete the following: If the price of a portrait during Month 21 is $10, what would you predict for sales in Month 21?