Answer:
x = 16
Explanation:
First you have to know the max degrees in this figure
Since the shape is a right triangle, then the max degrees is 180°
Now that box in the triangle indicates that the angle measures 90°
180° - 90° = 90°
so for both missing angles, we're going to create a equation that satisfy to 90°

First subtract the 26 from both sides (on 90 and on the equation)
(We're left with this)
64 = 3x + x
64 = 3(16) + 16
64 = 48 + 16
64 = 64
x = 16