Each rear tire on an experimental airplane is supposed to be filled to a pressure of 40 pound per square inch (psi). Let X denotes the actual air pressure for the right tire and Y denotes the actual air pressure for the left tire. Suppose that X and Y are random variables with the joint density
(a) Find k.
(b) Find P(30 < X < 40 and 40 < Y < 50).
(c) Find the probability that both tires are under filled.