A computer bureau's telephone help desk is staffed by five people through the day. The bureau handles about 15 customers an hour and the average time it takes to deal with the problem is 15 minutes. Determine the Q' Characteristics, if arrivals are Poisson and servicing follows a negative exponential distribution.

The operations manager believes that customers will be aggrieved if they have to wait for more than two minutes for their calls to be answered, How many additional staff should she recruit?