A multiple regression analysis was performed to determine the relationship between the satisfaction rating for a new candy bar and the amount of chocolate used and the amount of caramel used. What is the mean value of the satisfaction rating, if the estimated regression equation is y=7.6+2.1X1-0.9X2, the amount of chocolate (x1 ) used is 0.35 ounce, and the amount of caramel (x2 ) used is 0.15 ounce?