Answer:
∠ 1 = 50°
Explanation:
The sum of the interior angles of a polygon is
sum = 180° (n - 2) ← n is the number of sides
here n = 5 , then
sum = 180° × 3 = 540°
sum the 4 angles of the polygon and equate to 540°
let the unknown interior angle be x
x + 100° + 120° + 100° + 90° = 540° , that is
x + 410° = 130°
∠ 1 and x are adjacent angles on a straight line and sum to 180° , so
∠ 1 = 180° - 130° = 50°