A three stage service process is defined as follows:

Stage

$1$

$2$

$3$

Process Coefficient of Variation $($cp$)$

$1$

$0\mathrm{.}7$

$0\mathrm{.}4$

Average Processing Time $($minutes$)$

$5$

$12$

$8$

Number of Workers

$3$

$5$

$4$

If $24$ customers arrive per hour. What is the average customer time at stage $2($in minutes $-$ don$$t include time from stage $1)?$