Question

What is the answer for the missing variable

Answer 1

Well that's a right angle so it has to be 90 degrees. 90 - 53 = 37 , so that's the angle of 5x - 3.
Now you can work it out like this to find x:

5x - 3 = 37
*add 3 to both sides*
5x = 40
*divide both sides by 5 to get x alone*
x = 8