Consider the model y = b0 + b1 x1 + b2 x2 + b3 x3 + e where x1 is a quantitative variable and x2 and x3 are dummy variables describing a qualitative variable at three levels, using the coding scheme x2 = e 1 if level 2 0 otherwise x3 = e 1 if level 3 0 otherwise The resulting least squares prediction equation is yn = 44.8 + 2.2x1 + 9.4x2 + 15.6x3

a. What is the response line (equation) for E(y) when x2 = x3 = 0? When x2 = 1 and x3 = 0? When x2 = 0 and x3 = 1?

b. What is the least squares prediction equation associated with level 1? Level 2? Level 3? Plot these on the same graph.