Problem 4
x = interior angle
y = exterior angle
x = 3y since "each interior angle...is three times the measure of each exterior angle"
The interior and exterior angles are supplementary, meaning,
x+y = 180
3y+y = 180
4y = 180
y = 180/4
y = 45
So we know that
n = 360/y
n = 360/45
n = 8
You are correct in saying that this is an octagon
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Problem 5
x = measure of missing angles
Find the sum of the interior angles
S = 180*(n-2)
S = 180*(5-2)
S = 540
The five interior angles add up to 540 degrees
Add up the five angles, set equal to 540, then solve for x
90+90+90+x+x = 540
2x+270 = 540
2x+270-270 = 540-270
2x = 270
2x/2 = 270/2
x = 135
So you have the correct answer of choice C) 135 degrees
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Problem 6
S = 180*(n-2)
S = 180*(6-2)
S = 180*4
S = 720
You have the correct answer. Nice work on all three correct answers.