Let the length of the diameter be d and radius be r, thus to solve for d we proceed as follows:
r²+31²=(r+15)²
solving for d we solve for r
r²+961=r²+30r+225
putting like terms together we obtain:
r²-r²+961-225=30r
736=30r
solving for r
r=24.53
thus
d=24.5333×2
d=49.067~49.1
Answer is D. 49.1
