Please assist with proving the below theorems (mean and variance of each)

If Y is a chi-square random variable with v degrees of freedom, then H = E(Y) = v and of= V(Y) = 2v. Apply Theorem 4.8 with a = v/2 and 8 = 2. If Y is an exponential random variable with parameter B, then H = E(Y) = 8 and o' = V(Y) = $2. The proof follows directly from Theorem 4.8 with a = 1