The exterior angle is = to the 2 interior angles.
83 = (9x + 4) + (4x + 1) Remove the brackets
83 = 9x + 4 + 4x + 1 Group the like terms
83 = 9x + 4x + 4 + 1 Add the like terms.
83 = 13x + 5 Subtract 5 from both sides.
78 = 13x Divide by 13
78 / 13 = x
x = 6
So They want the angles
9x + 4 = 9*6 + 4 = 58
4x + 1 = 4*6 + 1 = 25
When you add these two together you should get 83. Do you?