.123x1 5.09x2  .0709x3

.001x4

a. According to this model, what is the mean y value if x1 3200 and x2 57?

b. For this particular model, does it make sense to interpret the value of a b2 as the average change in tar content associated with a 1-degree increase in gas inlet temperature when rotor speed is held constant?

Explain.