2 right angles

1. Add (2x-11) and 51 together and set them equal to 90

2. Subtract 11 from 51 and you get 40

3. Subtract 40 from 90 and you get 50, then divide 50 by 2

4.  x=25

5. Plug in 25

6. Add 39 and 51 and you get 90