Need help with Graham's Law of Effusion Problem!?

Question

During an effusion experiment, it took 75 sec. for a certain number of moles of an unknown gas to pass through a tiny hole. Under the same conditions, the same number of moles of oxygen gas passed through the hole in 30 sec. What is the molar mass of the unknown gas? Show your work please.

Answer 1

The equation is that the rates of the 2 gases is inversely proportional to the sq. root of the masses

The ratio of the rates is 75/30.

The molecular mass of oxygen is 32.

Put into the equation and solve for the missing molecular mass