NATSUNO is correct. The answer is 16.
Basically, if the line is straight, it will equal 180.
So your equation should be:
18x - 215 + 5x + 27 = 180 (it could also be (5x + 27 + 18x - 215 = 180).
Once you got that down, add your like terms: 18x + 5x and -215 + 27 You should get 23x and -188.
You want to solve for x, so get x alone by adding -188 to 180.
It looks like this: 23x - 188 = 180
+188 +188
Now you’re left with: 23x = 368. Divide 368 by 23x, and x = 16.