What do you know about inscribed angles? After all that is the essence of this exercise.
$\displaystyle \angle ABD$ is the third angle of a right triangle and it is also an inscribed angle.
From its measure you can get the measure of $\displaystyle \text{arc}(AD)$.
From that you can get the measure of $\displaystyle \text{arc}(DAB)$.
Which gives you the measure of $\displaystyle x$.