The average number of calls received by a switchboard in a 30-minute period is 15

a. What is the probability that between 10:00 and 10:30 the switchboard will receive exactly 10 calls?

b. What is the probability that between 10:00 and 10:30 the switchboard will receive more than 9 calls but fewer than 15 calls?

c What is the probability-that between 10:00 and 10:30 the switchboard will receive fewer than 7 calls?

Not really Sure how to set up.