can anyone help

Again, suppose Bank " A " has only one teller. The expected total time a consumer spends at this bank, CT, is 40 minutes and the average effective process time of the teller, te, is 20 minutes. Assume that the coefficient of variation of interarrival times, ca, and coefficient of variation of effective process time, ce, are both equal to one. The total busy time of the teller in an 8 -hour shifts is: 8 hours 4 hours 6 hours 7 hours