UKMT Junior Mathematical Challenge, 2015

The four straight lines in the diagram are such that $VU = VW$. The sizes of $\angle UXZ$, $\angle VYZ$ and $\angle VZX$ are $x^\circ$, $y^\circ$ and $z^\circ$. Which of the following equations gives $x$ in terms of $y$ and $z$?

(A) $x = y - z$ (B) $x = 180 - y - z$ (C) $x = y - \dfrac{z}{2}$ (D) $x = y + z - 90$ (E) $x = \dfrac{y - z}{2}$