Answer:
x = 21
Step-by-step explanation:
The sum of the interior angles of a polygon is
sum = 180° (n - 2) ← n is the number of sides
Here n = 12 , then
sum = 180° × 10 = 1800°
Each of the 12 interior angles = 1800° ÷ 12 = 150
Then
7x + 3 = 150 ( subtract 3 from both sides )
7x = 147 ( divide both sides by 7 )
x = 21
