To calculate the rates of effusion we apply the Graham's Law of Diffusion of Gases.
The law relates the rate of diffusion or effusion of a gas to the type of molecule in the gas.
It is expressed as "the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molecular mass or density at constant temperature and pressure".
A gas with low molecular mass can diffuse or effuse more rapidly than one with high molecular mass under similar conditions.
By this, we can express a mathematical relationship to solve for the molecular masses of the gases.