$4.$ A service counter employs two servers. On average a server requires $8$ minutes to process a customer and service times Has a coefficient of variation of $1($CV $1).$ Customers arrive at the counter at the rate of $12$ per hour on average with a coefficient of variation of $1($CV $1).$

The service rate per server for this system is

Select one:

a$.7\mathrm{.}5$ customers per hour

b$.3\mathrm{.}75$ customers per hour

c$.16$ customers per hour

d$.8$ customers per hour