Vector Spaces & Bases · Medium problem

Let $U=\operatorname{span}\{(1,0,1)\}$ and $W=\{(x,y,z): x+z=0\}$ in $\mathbb{R}^3$, so $\mathbb{R}^3 = U\oplus W$. Write $(5,3,1) = u + w$ with $u\in U,\ w\in W$, and find the first coordinate of $w$.