Can I please have help.

4. Suppose a shop has two cashiers and one line of customers waiting to be served. The time for each cashier to serve the customer is an exponential random variable with _ = 1/4 and afterwards a customer leaves the store. Suppose both cashiers are busy with customers A and B, and customer C is the first in line to be served. What is the probability that among A, B, and C, C will not be the last to leave the store? Explain carefully. This question does not require extensive calculations