we know that
the figure VGP is a right triangle
VP-------> is the radius of the circle
so
Applying the Pythagoras Theorem
VP²=VG²+PG²---------> VP²=12.2²+13.1²-------> VP²=320.45-----> VP=17.9 in
radius is equal to VP
so
r=17.9 in
therefore
the answer is
the radius of the circle is 17.9 in