A small diner has one employee and a counter with seating for $8$ customers. The diner does not

package food for takeout. Customers arrive at the diner at the rate of $20$ per hour $($Poisson

distributed$).$ Service times are exponentially distributed and average $24$ per hour. Customers that

arrive when all seats are taken do not enter the diner. What is the average time a customer spends

waiting?

$2\mathrm{.}5$ minutes

$3\mathrm{.}0$ minutes

$24$ minutes

$6\mathrm{.}44$ minutes