Solution:

a^2 + b^2 = c^2

where

"a" is the nearest distance between the center and a point in a chord

"b" is the half the measurement of the chord

and "c" is the measurement of the radius

next is input the numbers given

8^2 + (30/2)^2 = c^2

c^2 = 64 + 225

c^2 = 289

c = 17 cm