At ${\text{27}}^{\text{o}}{\text{C, H}}_{\text{2}}$ gas is leaked through a tiny hole into a vessel for 20 minutes. Another unknown gas, at the same temperature and pressure, as that of ${\text{H}}_{\text{2}}$, is leaked through the same hole for 20 minutes. After the effusion of the gases the mixture exerts a pressure of 6 atm. If ${\text{H}}_{\text{2}}$ is 0.7 mol and volume of vessel is 3 litre, calculate molecular weight of the unknown gas.