The sum of the interior angles of the polygon is 20 right angles. how many sides does the polygon have?

We have a polygon whose the sum of interior angles is 20 right angles (the measurement of each right angle is 90°), that means
the sum = 20 × 90°
the sum = 1800°

The sum of interior angles on any polygon could be determined using formula
sum = (n - 2) × 180°
n stands for the number of sides the polygon has

sum = (n - 2) × 180°
1800° = (n - 2) × 180°
1800°/180° = n - 2
10 = n - 2
n = 12

The polygon has 12 sides