Verified answer

The idea is to reduce the problem to standard temperature and pressure, obtaining an equivalent volume. Then, since you know that one mole of gas occupies 22·4 litres at STP (being a gas without strong intermolecular attractions, in particular, well above its boiling point), you have V/22·4 moles of the gas. Knowing the chemical formula for methane, and the atomic weights, you can determine how much one mole weighs.