Let y = wear life of a bearing, , and x1 = oil viscosity, x2 = load. Suppose that the mu...

Let y = wear life of a bearing, , and x₁ = oil viscosity, x₂ = load. Suppose that the multiple regression model relating life to viscosity and load is

a. What is the mean value of life when viscosity is 40 and load is 1100?

b. When viscosity is 30, what is the change in mean life associated with an increase of 1 in load? When viscosity is 40, what is the change in mean life associated with an increase of 1 in load?