Let $U=\langle(1,0,1)\rangle$. Determine the equations of the orthogonal subspace of $U$

Question

Let $U = \langle(1,0,1)\rangle$. Determine the equations of the orthogonal subspace of $U$ and an orthonormal basis of it. Obtain an expression for the vector $v = (-8, 3, 5)$ of the form $v = x+ y$, $x$ is in $U$ and y is in the orthogonal of $U$.

Thanks very much. I have been trying to do it but I don't think is right.