Three estimates were $12,6,$ and $15,$ not given in any order. What is the PERT? $($Hint: optimistic is whatever the smallest estimate is$,$ pessimistic is the largest number, and the third number is "most likely"$)$ Pick closest answer.

$11\mathrm{.}5$

$8\mathrm{.}5$

$13\mathrm{.}0$

$23\mathrm{.}0$