So it may be a long process, but the way i solved this problem was to first find the measure of one interior angle, then subtract that from 180 (supplementary angles) to get the measure of x.
HOW TO:
1) Find measure of ONE interior angle (keep in mind that, as labeled in the diagram, each interior angle is the same measure):note that n stands for the number of sides.
(n-2)180/n
(5-2)180/5
(3)180/5
540/5
108
So the measure of ONE interior angle is 108 degrees.
2) Now subtract 108 from 180 to get the measure of x.
180-108 = 72
Thus, the measure of x is 72 degrees.