This GRE Math practice problem tests your understanding of angle relationships in a triangle.

In the figure above, $\overline{AB} \perp \overline{BC}$, and $\overline{AB} = \overline{AD}$. What is $y$ in terms of $x$ ?

- $\quad x-90$
- $\quad 2x-90$
- $\quad 90-x$
- $\quad 90-2x$
- $\quad \dfrac{x}{2}$