#12: #13:
x + 37 + x + 67 + 90 = 180 60 + 22x + 4 + 15x + 5 = 180
194 + 2x = 180 69 + 37x = 180
- 194 - 194 - 69 - 69
------------------------ ----------------------------
2x = -14 37x = 111
------ -------
2 2 x = 3
x = -7
#14: 55 + x + 74 + 54 = 180 #15: 40 + 2x = 180
183 + x = 180 - 40 - 40
- 183 - 183 ---------------------------
--------------------------- 2x = 140
x = -3 ----- ------
2 2
x = 70
16). 40 + 8x + 4 + 3x + 4 = 180
48 + 11x = 180
- 48 - 48
----------------------------
11x = 132
------- -------
11 11
x = 12
* I believe that the answer to #11 is x = 7, but I'm not fully sure.