In the magic square shown, the sums of the numbers in each row, column, and diagonal are the same. Five of these numbers are represented by $v,w,x,y,$ and $z$. Find $x+y$.

$\begin{array}{ccc}\text{v}& 15& \text{w}\\ 25& \text{x}& \text{y}\\ 18& \text{z}& 12\end{array}$