Rates of Effusion

Hello Everyone!

This is my first time posting on these forums. I am a student that is currently taking general Chemistry in college -- this is my first semester. During one of our online quizzes, we were posed with the following question:

Oxygen gas effuses at a rate of 0.0140 moles/sec through a small hole. A second gas effuses through the same hole at 0.0174 moles/sec at the same temperature, calculate the molar mass of the gas.

A.) 28

B.) 77

C.) 63

D.) 50

E.) 51

Here is my work:

R_O2= .0140

R_X= .0174

R_O2 .0140 / R_X .0174 = √[Molar Mass _X / Molar Mass _O2] = √[Molar Mass _X / 32]

(.0140/.0174)² = Molar Mass _X / 32

32(.0140/.0174)² = Molar Mass _X

20.72 = Molar Mass _X

Here is my question:

Where in my process did I go wrong? Looking back at it now, I can not spot a mistake. I used Graham's Law of Effusion (hopefully correctly).

~ Thanks for your help in advance!