Find the diameter, round to the nearest tenth 49.1 55.5 60.7 68.2

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

I’m not absolutely sure but i think it’s 7x6x5x4x3x2=5040 because as the first character you can take any of the 7 given then you are left with 5 then 6 then 4 etc.