36. A certain queuing system has a Poisson input with a mean arrival rate of two calling units per hour.

The service time distribution is exponential with a mean of0.4 hour. The marginal cost of providing each server is Rs 4 per hour, where it is estimated that the cost which is incurred by having each calling unit idle (i.e. in the queuing system) is Rs 100 per hour. Determine the number of servers that should be assigned to the system in order to minimise the expected total cost per hour. (MBA, Delhi, 1974)