A new strip mall is being considered and the developers want to determine how many parking spaces

there should be$.$ It is assumed that if the lot is full, an arriving car will leave. Cars arrive at a rate of

$15//$ hour. The average time a customer spends shopping is $30$ minutes. Assume the interarrival times and the shopping times are exponentially distributed. Assume the average shopper purchases $$150$ worth of merchandise and also assume the mall is open $12$ hours$/$day$,350$ days$/$year$.$

a$.$ If there are $10$ spaces, determine the throughput rate of cars departing after completing shopping, the expected number of cars in the parking lot and the rate of lost revenue due to cars leaving because they could not find a space to park.

b$.$ Assume the cost to create a parking spot is $$2500.$ Assuming a $5-$year horizon and an internal interest rate of $15\%,$ how many spots should be built to minimize the combined construction and lost revenue costs?

Im pretty sure the model for part a is an M$/$M$/1//10$ but everyone else on chegg has it as an M$/$M$/1$ but that should be incorrect because there is a capacity of $10.$