Answer:
x = 100°
Step-by-step explanation:
The polygon has 6 sides, meaning it's a hexagon. In the picture you can see the following steps under #1:
(6-2) x 180° = 4 x 180 = 720°
720 is the total amount that all the angles should add up to, including the missing number x.
To solve for x add all of the angles up:
120 + 156 + 145 + (x + 9) + x + 90 = 720
520 + 2x = 720 (subtract 520 from both sides)
-520
2x = 200 (divide 200 by 2 to have x on its own)
x = 100°
To make sure it's correct, plug in the value (100°) for x in the original equation to check the answer:
120 + 156 + 145 + 100 + 9 + 100 + 90 = 720
720 = 720 Correct