Consider the following regression model:

y = b0 + b1x1 + b2x2 + e where:

x1 = A quantitative variable x2 = e 1 if x1 6 20 0 if x1 Ú 20 The following estimated regression equation was obtained from a sample of 30 observations:

yn = 24.1 + 5.8x1 + 7.9x2

a. Provide the estimated regression equation for instances in which x1 6 20.

b. Determine the value of yn when x1 = 10.

c. Provide the estimated regression equation for instances in which x1 7 20.

d. Determine the value of yn when x1 = 30.