1. A small bank is trying to determine how many tellers to employ. The total cost of employing a teller is $10 per hour, and a teller can serve an average of 90 customers per day. An average of 120 customers per day arrive at the bank, and both service times and interarrival times are exponential. if the delay cost per customer-hour is $20 and bank is working 8 hours per day, 

How many tellers should the bank hire?