Refer to the previous exercise.

Let x1 = 1 for the advertisement and 0 otherwise, x2 = 1 for Muzak and 0 otherwise, and x1 = x2 = 0 for classical music. Likewise, let x3 = 1 for repeating in 10-minute cycles and x3 = 0 for repeating in 5-minute cycles. The display shows results of a regression of the telephone holding times on these indicator variables.
Regression for telephone holding times

a. State the prediction equation. Interpret the parameter estimates.
b. Find the estimated means for the six groups in the two-way cross-classification of message type and repeat time.
c. Find the estimated difference between the mean holding times for 10-minute repeats and 5-minute repeats, for a fixed message type. How can you get this estimate from a coefficient of an indicator variable in the prediction equation?

Telephone holding times by type of recorded message and repeat time Repeat Time Message Advertisement Muzak Classical Ten Minutes 8, 11, 2 1, 4, 3 13, 8, 15 Five Minutes 5, 1 0, 6 7,9 Predictor Coef SE Coef T Constant xl x2 x3 8.867 1.77 4.99 -5.000 2.051-2.44 -7.600 2.051-3.71 2.556 1.709 1.50 0.000 0.033 0.003 0.163