In $△ABC$, $AB=17$, $AC=8$, and $BC=15$. Points $M$ and $N$ lie on $AC$ and $BC$, respectively, with $CM=CN=3$. Points $J$ and $K$ are on $AB$ so that $MJ$ and $NK$ are perpendicular to $AB$. What is the area of pentagon $CMJKN$? Refer to the diagram below.