Graph Algorithms · Medium problem

A project has tasks $s,r,t,u,v,w,x$ with durations (days) and prerequisites $s \to r$ ($3$), $s \to t$ ($2$), $r \to u$ ($4$), $t \to u$ ($5$), $t \to v$ ($2$), $u \to w$ ($3$), $v \to w$ ($2$), $t \to x$ ($1$), $x \to w$ ($2$). Each number is how many days that task itself takes, and the project (ending at $w$) finishes in $10$ days at the earliest. By how many days could task $x$'s completion be delayed from its earliest possible finish without delaying the whole project (that is, what is $x$'s slack)?