Suppose that X is a random variable with mean 20 and standard deviation 4. Also suppose that Y is a random variable with mean 40 and standard deviation 7. Find the mean and the variance of the random variable Z for each of the following cases. Be sure to show your work.
(a) Z = 40 - 5X
(b) Z = 15X - 20
(c) Z = X + Y
(d) Z = X - Y
(e) Z = -2X + 3Y