What pressure? What temperature? If you have P and T you can use PV = nRT and solve for volume in L. If you don't have those, you make the assumption that you have STP conditions (standard temperature and pressure) and under those conditions 1 mol of any ideal gas (and you assume CH4 is ideal) will occupy 22.4 L. So 2.54 mol x 22.4 L/mol = ? L.
