States of Matter

At STP, a closed vessel contains 1 mole each of He and CH4. Through a small hole, 2L of He and IL of CH4 was escaped from vessel in ' t ' minutes. What are the mole fractions of He and CH4 respectively remaining in the vessel? (Assume He and CH4 as ideal gases. At STP one mole of an ideal gas occupies 22.4L of volume)