aniel arrives at a post office with $2$ counters. All counters are busy at the

moment that Daniel arrives. Therefore, Daniel has to wait at the queue in which there

are already three customers waiting for services; in other words, Daniel is in the $4$th

place of the queue. You are given:

$$ Counter $1$ handles $1$ customer per $3$ minutes.

$$ Counter $2$ handles $2$ customers per $12$ minutes.

Calculate Daniel$$s expected total waiting time plus service time, in minutes, until he is

finished being served.

Solution: $12$