Triangle $△PQR$ is similar to triangle $△STU$, such that $P$, $Q$, and $R$ correspond to $S$, $T$, and $U$ respectively. The length of each side of triangle $△STU$ is 3 times the length of its corresponding side in triangle $△PQR$. The measure of side $PQ$ is 8. What is the measure of side $ST$?