If X is a Negative Binomial random variable with parameters p and r, then find the moment

Question:

If X is a Negative Binomial random variable with parameters p and r, then find the moment generating function of X.
In Exercise 1
P(X = x) = px(x) = (1- p)x-lp
For x = 1, 2, 3,...,
and pX(x) = 0 otherwise), then find the moment generating function of X.