Please note that there are two employees, not one, so I wanted to clarify that so that the solution can be relied upon

A new shopping mall is considering setting up an information desk operated by two employees. Based on information obtained from similar information desks, it is believed that people will arrive at the desk at the rate of 20 per hour. It takes an average of 4 minutes to answer a question. It is assumed that arrivals are Poisson and answer times are exponentially distributed. (a) Find the proportion of the time that the employees are busy. (b) Find the average number of people waiting in line to get some information. (c) Find the expected time a person spends just waiting in line to have his question answered