Data Sufficiency (DS) | Re: Two bicycle wheels, A and B, start rotating at constant speeds at the

I think the answer should be C.

Statement 1: NOT SUFFICIENT. Assuming the speed of the wheel A= x and B=3x, we cannot determine the individual actual speeds (which are required to answer this question).

Statement 2: NOT SUFFICIENT. The average speed also doesn't help to determine the individual actual speeds (which are required to answer this question).

Putting Statement 1 and Statement 2 together
The individual speeds can be determined by the formula: Average Speed= 2*S1*S2/(S1+S2)
40= 2*x*3x/(x+3x)
x= 80/3 revolutions per min (Speed of A)
3x= 80 revolutions per min(Speed of B)

Relative Distance= 6 rotations (given in the question stem)
Relative Speed= 80-80/3 revolutions per min (calculated above)

Time= Relative Distance/Relative Speed
= 6*60/(160/3)
= 6 3/4 secs

I am not sure about the last calculation part of Relative Time. Can someone please cross-check the logic and the calculation of my explanationhere?