Lines & Planes in Space · Hard problem

A point $P$ moves along the line $\mathbf r(t) = (1, 0, 2) + t\langle 1, 1, -1\rangle$, and a point $Q$ moves along the line $\mathbf s(u) = (0, 3, 1) + u\langle 1, 2, -1\rangle$. If $P$ and $Q$ are required to always have the SAME $x$-coordinate, find the minimum possible distance $PQ$.