States Of Matter

At STP, a closed vessel contains I mole each of He and $\mathrm{CH}_4$. Through a small hole, 2 L of He and LL of $\mathrm{CH}_4 \mathrm{WHS}$ escaped from vessel in ' $t$ ' minutes. What are the mole fractions of He and $\mathrm{CH}_4$ respectively remaining in the vessel? ( Assume He and $\mathrm{CH}_4$ as ideal gases. At STP one mole of an ideal gas occupies 22.4 L of volume.)