In the book Super Crunchers, author lan Ayres presents the model y̅ = 12.15 + 0.00117x1 + 0.0614x2 - 0.00386x3, where y represents the quality of a wine, x1 represents total rainfall in the winter prior to harvest (in inches), x2 represents the average temperature during the growing season (in degrees Fahrenheit), and x3 represents total rainfall during the harvest season (in inches).

(a) Interpret the slope coefficients of the model.

(b) Predict the wine quality rating of a wine where the total rainfall the winter prior to harvest was 8 inches, average temperature during the growing season was 58°F, and total rainfall during the harvest season was 2.9 inches.