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Question

Doc on call

A company has started a phone service that uses overseas doctors to provide emergency medical consultations. The responding doctors are based in a country with low wages but with a highly skilled pool of physicians. Responding to each call takes, on average, $15$ minutes. At any given time, there are $4$ doctors overseas on duty. Calls arrive every $5$ minutes on average $($standard deviation is $5$ minutes$).$ The company receives $$50$ from the patient's insurance company for each consultation. If one of the $4$ overseas doctors is available, the firm pays $$20$ to the doctor and makes $$30$ in profit. If no doctor is available overseas, the call is rerouted to the U$.$S$.$ where a local physician answers the question. A local physician is always available to take a call. In this case, the firm pays the $$50$ to the local physician, so there's no profit for the company. What is the additional revenue per hour obtained by having $10$ doctors overseas on duty at any given time,