Answer: There are 10 sides
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x = measure of each interior angle
y = measure of each exterior angle
We know that x = 4y as "each interior angle is four times the measure of each exterior angle"
The interior and exterior adjacent angles are supplementary
x+y = 180
4y+y = 180
5y = 180
5y/5 = 180/5
y = 36
If y = 36, then
n = 360/y
n = 360/36
n = 10