first, find the sum of interior angle of a pentagon (5-sided)

by using the formula 180(n - 2)

where n = 5

180(5 - 2) = 540°

the first 4 interior angles are already given:

90°

100°

110°

120°

add them

90 + 100 + 110 + 120 = 420

fifth angle = 540 - 420

fifth angle = 120°

Answer:

120°

Step-by-step explanation:

Since the sum of all interior angle of a convex pentagon is 540°,

90 + 100 + 110 + 120 + measure of the fifth interior angle = 540

we can represent the measure of the fifth interior angle as x

90 + 100 + 110 + 120 + x = 540

420 + x = 540

x = 540 - 420

x = 120

So we can conclude that the measure of the fifth interior angle is 120°.