First off,you need to understand that angles on a point = 360°,meaning that the sum of the angles above would be 360°.
What you need to to is to deduct the angles above from 360°,then you would find X.
Here's the equation:
360°-180°-26°-90°
=64°
Or as an alternative:
x+180°+26°+90°=360°
x=360°-180°-26°-90°
x=64°
thus the answer is x=64°
hope it helps!