#### Answer

$WX$ = $5$

#### Work Step by Step

In congruent polygons, vertices are named in the exact order of their matching vertices.
If $WXYZ$ is congruent to $PQRS$, then vertex $W$ corresponds to vertex $P$, vertex $X$ corresponds to vertex $Q$, vertex $Y$ corresponds to vertex $R$, and vertex $Z$ corresponds to vertex $S$.
Therefore, $WX$ is congruent to $PQ$, so $WX$ is equal to $PQ$. If $PQ$ is $5$, then $WX$ is also $5$.