The measure of an angle formed by two tangents = 1/2 the difference of the measure of the intercepted arcs.
Let the arc nearest the 72 degree angle be y, then the outer arc is 360 - y, so
72 = 1/2 (360 - y- y)
144 = 360 - 2y
-216 = 2y
y = 108
y = 108 is also the measure of the arc intercepted by the central angle x.
The measure of a central angle is equal to the measure of intercepted arc, so x = 108.