Answer:
D. x = 21
Step-by-step explanation:
So a straight line is equal to 180º and that's what we're trying to figure out here. Set both equations to equal 180, it should look like:
5x + 4x - 9 = 180
Now we just solve!
5x + 4x - 9 = 180
5x + 4x = 9x
9x - 9 = 180
+9 +9
------------------
9x = 189
Divide both sides by 9 to get x by itself.
189/9 = 21
x = 21
