Customers arrive to the checkout area of New Navy such that the interarrival rate is exponential with rate equal to $50$ customers per hour. At the checkout area, the service time of each customer is exponentially distributed with a mean of $12$ minutes. The store has hired $11$ cashiers to checkout customers and the checkout area consists of a single pool of cashiers with one common line in front of them.

a$.$ What is the service rate?