PLEASE SHOW WORK-I need to know how you got the answer

Scheduling Employees: Suppose you own a catering company. You hire temporary employees to act as servers from the local college. Not being the most reliable employees, there is an 80% chance that any one server will actually show up for a scheduled event. For a wedding scheduled on a given Saturday you need at least 5 servers.

1. (a) Suppose you schedule 5 employees, what is the probability that all 5 come to work?
2. (b) Suppose you schedule 7 employees, what is the probability that at least 5 come to work?
3. (c) How many employees should you schedule in order to be 99% confident that at least 5 come to work? Hint: There is no single formula for the answer to this problem, you should use some type of trial and error.