The answer is at the end of turn 3.
y=-3x-1
Is your answer if thats how you need it.
All the angles in a triangle equal 180 degrees so 128 + (5x+10) + 9x = 180
Group the like values to get 138 + 14x = 180
Subtract 138 from 180 to get 14x = 42
Divide 42 by 14 to get x = 3
Therefore x = 3
