some help with gamma and chi squared distribution?

Can anybody help me with these questions, Should be a matter of plugging values into gamma and chi squared distribution formuals, I think I'm doing them right but getting out of bounds answers. Thanks

Calls arrive at a switchboard according to a Poisson process with rate

= 42 per minute.

Find the probability that the 10th call arrives after 15 seconds and

before 20 seconds have elapsed.

Find the probability the time between the 5th and the 10th call is

greater than 10 seconds.

If 20% of calls are long-distance and 80% are local nd the mean time

between two long-distance calls, and the probability that the time

between two consecutive long-distance calls is less than 20 seconds.