Calls to the help line of a large computer distributor follow a Passion distribution with a mean

Question:

Calls to the help line of a large computer distributor follow a Passion with a mean of 20 calls per minute.
(a) What is the mean time until the one-hundredth calls?
(b) What is the mean time between call numbers 50 and 80?
(c) What is the probability that three or more calls occur within 15 seconds?
Distribution
The word "distribution" has several meanings in the financial world, most of them pertaining to the payment of assets from a fund, account, or individual security to an investor or beneficiary. Retirement account distributions are among the most...