Triangle $PQR$ is similar to triangle $LMN$ such that $P,Q,$ and $R$ correspond to $L,M,$ and $N$, respectively. The measure of $\angle P$ is $30^{\circ }$ and the measure of $\angle Q$ is $70^{\circ }$. If $PQ=\frac{1}{2}LM$, what is the measure of $\angle N$?