15-31 In a bank customers arrive in a Poison stream with mean 36 per hour. The

service time per customer is exponential with mean .035 hour. Assuming that the

system can accommodate at most 30 customers at a time, how many tellers should

be provided under each of the following conditions?

a) The probability of having more than 3 customers waiting is less than .20.

b) The expected number in the system does not exceed 3.