1. The problem statement, all variables and given/known data If M[X(t)] = k (2 + 3e^t)^4 , what is the value of k 2. Relevant equations M[X(t)] = integral ( e^tx * f(x) )dx if X is continuous 3. The attempt at a solution I tried differentiating both sides to find f(x), but since it is a definite integral from negative infinity to infinity this method doesn't work. Is this approach (trying to find f(x)) correct? If so, how should I proceed from here? Even if I expand (2 + 3e^t)^4 the resulting expression will be very convoluted and hard to work backwards with. Thanks!