Answer:
x = 45°
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 = 8 ( number of sides of an octagon ) , then
sum = 180° × 6 = 1080°
the interior angles of a regular octagon are congruent , so
∠ ABC = 1080° ÷ 8 = 135°
x and 135° are adjacent angles on a straight line and sum to 180° , then
x = 180° - 135° = 45°
