A company has a very large number of semiautomatic grinding machines. The

time each machine runs before needing service is exponential with a mean of $20$

minutes. The time an operator has to spend to get the machine working again is

also exponential, but with a mean of two minutes. At this time, in a work cell,

there is one operator per every four machines. You may use QTS to determine

the necessary MOPs below.

a$)$ Calculate the average number of machines that are operating per cell in

this configuration.