A continuous random variable X has probability density function f_X(x) = c exp(-2|x| + x). (a) Determine the value of c. (b) Determine the moment generating function M_X(t) of X, remembering to state the valid range for t. (c) Hence, or otherwise, determine the mean and variance of X. (d) Define the random variable Y := X^4. Give the probability density function for Y.