18)

The triangle on the right has angles $$31$$ and $$90$$ degrees. The third angle is $$180 - 90 - 31 = 59$$ degrees. The angle $$x$$ is part of the larger triangle. The larger triangle has angles $$59$$, $$90$$, and the angle at the top. The angle at the top is $$90 - 59 = 31$$ degrees. The angle $$x$$ is an exterior angle. The two opposite interior angles are $$31$$ and $$59$$. So, $$x = 31 + 59 = 90$$.
Answer: $$x = 90$$.