the pentagon has 3 angles which are each 140°. The other two interior angles are equal. calculate the size of one of these angles

60°

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 = 5 (pentagon), thus

sum = 180° * 3 = 540°

let x be the size of the equal angles

Sum the interior angles and equate to 540

(3 * 140) + 2x = 540

420 + 2x = 540 (subtract 240 from both sides)

2x = 120 (divide both sides by 2)

x = 60

Thus the size of 1 of the 2 equal angles = 60°