I'm going to do it by stoichiometry :
molar mass of CH4 is 16
and there are 4 H atoms in each CH4 so one mole CH4 consists of 4 x 6.022x10^23 H atoms
so :
4gr CH4 x (1mole CH4 /16 gr CH4) x (4 x 6.022 x 10^23 H atoms/1mole CH4) =
=6.022 x 10^23 H atoms
