The mean wait in a queuing system is $2\mathrm{.}9$ minutes and the mean wait in the queue is $1\mathrm{.}5$ minutes. The following must be true:

Group of answer choices

The mean service time must be $1\mathrm{.}4$ minutes.

The proportion of time the server is busy must be $0\mathrm{.}5$

None of the other choices

The mean inter$-$arrival time must be $1\mathrm{.}2$ minutes.