Solve for x. 17-22 help please. Explain

All the triangles' interior angle measurements add up to 180°.

Make #17-22 equal 180.

17) 80 + 4x + 11 + 45 = 180
       136 + 4x = 180
       4x = 44
       x = 11°

18) A square, or a right angle, indicates 90°.
      90 + 4x + 3 + 55 = 180
      148 + 4x = 180
      4x = 32
      x = 8°

19) 11x - 3 + 40 + 55 = 180
       11x + 92 = 180
       11x = 88
       x = 8°

20) 79 + 5x + 5 + 41 = 180
       125 + 5x = 180
       5x = 55
       x = 11°

21) 80 + 10x + 40 = 180
       120 + 10x = 180
       10x = 60
       x = 6°

22) 60 + 2x + 11 + 85 = 180
       156 + 2x = 180
       2x = 24
       x = 12°