For the multiple regression equation ŷ = 100 + 20x1 – 3x2 + 120x3:
a. Identify the y-intercept and partial regression coefficients.
b. If x1 = 12, x2 = 5, and x3 = 10, what is the estimated value of y?
c. If x3 were to increase by 4, what change would be necessary in x2 in order for the estimated value of y to remain unchanged?