With the information given, how can $x=45^\circ$? I just could not find a way it would be possible.
$x$ is not $45^\circ$.
Let $E$ be the point of the intersection of $\overline{AC}$ and $\overline{BD}$.
If $x=45$, then $\angle DEC= 45^\circ$ and due to vertical angles, $\angle AEB=45^\circ$.
If $\angle AEB=45^\circ$, then $\angle ABE=45^\circ$.
But, if this were true, $\triangle ABC$ is a $45-45-90$ triangle.
If this were true, then there would be no $\triangle DEC$, as points $B$ and $E$ would lie on the circumference of the circle.
The question must be referring to the angle at $D$. $\hat{BDC} =45^{\circ}$.
$x$ is not $45°$.
But angle $BDC$ surely is.
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Let $E$ be the point of the intersection of $\overline{AC}$ and $\overline{BD}$.
If $x=45$, then $\angle DEC= 45^\circ$ and due to vertical angles, $\angle AEB=45^\circ$.
If $\angle AEB=45^\circ$, then $\angle ABE=45^\circ$.
But, if this were true, $\triangle ABC$ is a $45-45-90$ triangle.
If this were true, then there would be no $\triangle DEC$, as points $B$ and $E$ would lie on the circumference of the circle.