CASE SCENARIO: DRIVER'S DONUTS

Driver's Donuts is a bakery and coffee shop that depends on morning comimuters for $80\%$ of its daily business. During the morning rush from $5$:$30$ a$.$m$.$ to $8$:$30$ a$.$m$.,$ an average of $35$ cars arrive at the Driver's Donuts drive$-$ through lane every hour, to purchase donuts and coffee through a single store window. The employee who staffs that window can serve each car in an average of $90$ seconds, although this speed is partially due to the fact that a second employee talks to the car behind the one being served, inputting that car's order so that the window employee knows the order and its cost when the second car arrives at the window. Without that assistance, it takes the window employee an average of $2$ minutes to serve any car, which is the practice outside of the morning rush hours, as customer traffic in the drive$-$through lane drops to an average of four cars an hour. Assuming that Driver's Donuts drive$-$through lane meets the assumptions of the M$/$M$/1$ model, answer the following questions.

Questions