Instead of performing a fixed number of Bernoulli trials, an experimenter performs trials until the first success

Question:

Instead of performing a fixed number of Bernoulli trials, an experimenter performs trials until the first success occurs. The number of successes is now fixed at 1, but the number of trials Y is now random. It can assume any of the values 1, 2, 3, and so on with no upper limit.
(a) Show that f(y) = qy-1p for y = 1, 2, . . .
(b) Find the probability of 3 or fewer trials when p = .5.