Answer:
144°
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 ( octagon ), hence
sum = 180° × 6 = 1080°
let the measure of 1 congruent angle be x
Then sum the 8 angles and equate to 1080
100 + 120 + 140 + 5x = 1080
360 + 5x = 1080 ( subtract 360 from both sides )
5x = 720 ( divide both sides by 5 )
x = 144
Thus each of the 5 congruent angles is 144°
