$19$

$2$ points

While executing DFS$,$ you pop a vertex $u$ from the Stack. We find that $u$ is not already closed and $u$ has an edge to $x.$ Currently, level $[u]=5,$ level $[x]=4.x$ is alreadv closed. and $x$ is on the stack. After the edge is relaxed, level $[x]=$ and $x$