Consider an Espresso Stand with a Single Barista

Consider an espresso stand with a single barista.Customers arrive to the stand at the rate of 28 per hour according to a Poisson distribution.Service times are exponentially distributed with a service rate of 35 customers per minute.If the arrival rate remains at 28 customers per hour and the stand's manager wants to have the average time a customer spends in the system (i.e. ,wait time and service time) to be a maximum of 6 minutes on average,then the service rate must

A) decrease by 2 to 33 customers per hour.
B) decrease by 3 to 32 customers per hour.
C) increase by 3 to 38 customers per hour.
D) increase by 2 to 37 customers per hour.