Hi all, I very much appreciate if someone can help me with this exercise:

A typist get work according to a process poisson, with an average of four jobs per hour. The works are typed according to the order of arrival, and the average job requires 12 minutes of time of worker; apparently the actual work time is exponentially distributed around this average. Determine:
a) The probability that a job will be completed in less than 45 minutes after arrival.
b) The probability that the typist complete all work by the end of the day.
c) The probability that the job would lead to the typist least 12 minutes.

Solution: 0528; 0.2; 0632 respectively.

I have not so far addressed.