Question

How to solve for x?

Answer 1

So 128 and the angle right next to it which is inside the triangle and supplementary angles, meaning that they both add up to 180. so you can do 180 - 128 is 52. so then 52 and 47 are both inside the triangle and so is x. add both 52 and 47 and then subtract it by 180 to find x. 
x is 81
hope this helps!

Answer 2

Multiply both sides by x so that x will be in the numerator