A straight line is 180°, so you can do:
109 + ? = 180 (? is the top angle of the triangle)
? = 71°
Because the triangle is an isosceles triangle, the other angle is 71° too.
71 + 71 + ? = 180
? = 38
You subtract 38 with 90 to find the other angle.
90 - 38 = 52°
To find ∠2 you subtract 52 with 180.
180 - 52 = 128
∠2 = 128
128 = 11x + 18
110 = 11x
10 = x
