Question $1$ to Question $5$ is based on this problem:

Graft Hair Salon has three barbers to provide service in a neighborhood

of downtown of Santa Fe$.$ Customers arrive at a rate of $8$ customers per

hour, and the average service time of each person is $15$ minutes. The

interarival time and service time of customers are exponentially

distributed.

Which of the following models is most suitable for the problem?

$\frac{M}{M}\frac{?}{s}$

$\frac{M}{M}\frac{?}{1}$

M$/$G$/1$

M$/$D$/1$