V CH4 = 448 L
n CH4 = V CH4 / 22.4 (L/mol) =>
nCH4 = 448 L/ 22.4 (L/mol) = 2 mol
NA = 6.023 x 10^23 molecule/mol
nr molecule CH4 = n CH4 x NA =>
nr molecule CH4 = 20 mol x 6.023 x 10^23 = 1.0246 x 10^25 molecule CH4
20 mol CH4 .... 1.0246 x 10^25 molecule CH4
n mol H2O .... 1.0246 x 10^25 molecule H2O => n moli H2O = 20 mol
m H2O = 20 mol x 18 g/mol = 360 g H2O