How much is x ?
You have similar triangles: Triangle $\displaystyle BDE$ is similar to triangle $\displaystyle BAC$.
So:
$\displaystyle \frac{BD}{AB}=\frac{DE}{AC}$,
or:
$\displaystyle \frac{AB-x}{AB}=\frac{x}{AC}$.
From which you should be able to find $\displaystyle x$.
RonL