Answer x = 13
Step by step
First figure out the angle sum for the figure you are looking at.
This is a Square, a four-sided polygon that has all its sides equal in length, and all the interior angles are equal to 90 degrees. The sum of all angles is 360. The length of the diagonals is also equal.
So if ∠3 and ∠4 = 90, split that in half.
So ∠ 3 is 45 degrees.
Your equation to find x
∠3 = 4x - 7
45 = 4x - 7
Add 7 to both sides to isolate variable
45 + 7 = 4x -7 +7
52 = 4x
Divide both sides by 4 to solve for
52/4 = 4/4x
13 = x