So first you create an equation using the values, because you know angles in a triangle add up to 180. It should look something like:
90 + 5x - 2 + 3x + 4 = 180
Then you'd simplify the parts on the left:
92 + 8x = 180
And then you solve:
92 + 8x = 180
- 92
8x = 88
÷ 8
x = 11
Hope this helps!