operations research2 questions

please solve them showing the solution

Customers arrive at a bank facility at the average rate of 20 per hour, according to a Poisson distribution. There is only one teller window capable of serving 25 customers per hour on the average with exponential service times. Customers form one line, going to the available teller on the bases of FCFS. The bank facility has space sufficient only for a total queue size of 27 clients. If the space yard is full, new arriving clients balk to other facilities. The proportion (probability) of time that the space yard of the system is full is a. Less than or equal to 0.02% of the time b. Greater than 0.02% but s 0.04% of the time C. Greater than 0.04% 30.06% of the time d. Greater than 0.06% of the time Customers arrive at a bank facility at the average rate of 20 per hour, according to a Poisson distribution. There is only one teller window capable of serving 25 customers per hour on the average with exponential service times customers torm one line, going to the available teller on the bases of FCFS. The bank tacility has space sufficient only for a total queue size of 27 clients. If the space yard is tuil new arriving clients bak to other facilities. The average number of customers waiting in the system is a less than or ecucito 4 customers b. Greater than bus customers C. Greater than customers buts customers d Greater than custom