So for a hexagon, the sum of all interior angles is 720°, all we need to do is add all the angles up and set it to 720 to get angle B.

Firstly, combine like terms to get 
Next, subtract 612 on each side, and your answer should be 
I beilieve it’s 11 I’m not 100% certain though
4x-30=180
180-30
4x=150
150/4
37.5
x=37.5