Patients visit a doctor in accordance with a Poisson process at the rate of 8 per hour, and the time doctor takes to examine any patient is...

Patients visit a doctor in accordance with a Poisson process at the rate of 8 per hour, and the time doctor takes to examine any patient is exponential with mean 6 minutes. All arriving patients attended by the doctor. The expected total time spent (including the service time) by any patient who visits the doctor is given by 

No need of any explanation.