An experiment to evaluate the effects of certain variables on soil erosion was performed on 10-foot-square plots of sloped farmland subjected to 2 inches of artificial rain applied over a 20-minute period. The data and related ANOVA table are as follows:

a. Compute R2, and comment on the fit of the model.
b. The fitted model involving all three independent variables is given by Ŷ = -1.879 + 77.326X1 + 1.559X2 - 23.904X3. Compute and compare observed and predicted values of Y for plots 1, 5, and 7.