Triangle $△JKL$ is similar to triangle $△MNO$, such that $J$, $K$, and $L$ correspond to $M$, $N$, and $O$ respectively. The length of each side of triangle $△MNO$ is $1.5$ times the length of its corresponding side in triangle $△JKL$. The measure of side $JK$ is 12. What is the measure of side $MN$?