In a single phase single server service process where both interarrival time and service times are exponentially distributed, it can be assumed that the total time that a customer spends in the process is also exponentially distributed. Suppose the total time the customers spend in a pharmacy is exponentially distributed with mean of 4 minutes. The pharmacy has promised to fill all prescriptions in 9 minutes.

1. What percentage of the customers cannot be served within this time limit?

The potential answers are:

A: 8.21%

B: 4.98%

C: 13.53%

D: 9.07%

E: 10.54%