Statistics (Poisson, Exponential Distribution)

Here is the question-

Let X equal the number of students who use a college card catalog every 15 minutes. Assume that X has a Poisson distribution with mean 5. Let W equal the time in minutes between two student arrivals. Then W has an exponential distribution with ? = 3.

Find P(W > 6) and P(W > 12| W > 6)