REmember that the sum of the interior angles in any polygon is equal to
S=180(n-2)
where
n is the number sides
In this problem
n=20 sides
so
S=180(20-2)
S=3,240 degrees
Divide by the number of sides to obtain the measure of each interior angle
3,240/20=162 degrees
To obtain the measure of exterior angle
180-162=18 degrees
therefore
answer is
Measure of each interior angle is 162 degrees
Measure of each exterior angle is 18 degrees