14.7 The article “The Influence of Temperature and Sunshine on the Alpha-Acid Contents of Hops” (Agricultural Meteorology [1974]: 375–382) used a multiple regression model to relate y  yield of hops to x1  average temperature (C) between date of coming into hop and date of picking and x2  average percentage of sunshine during the same period. The model equation proposed is y 5 415.11 2 6.60x1 2 4.50x2 1 e

a. Suppose that this equation does indeed describe the true relationship. What mean yield corresponds to an average temperature of 20 and an average sunshine percentage of 40?

b. What is the mean yield when the average temperature and average percentage of sunshine are 18.9 and 43, respectively?

c. Interpret the values of the population regression coefficients.