Hello, You can start by converting you pressure from torr to atm. Or look up and R=constant with torr units. once you did that, use the formula PV=nRT, in order to find n=quantity of moles. Then, use the molar mass of CH4, to find the mass using this relationship n(mol)=mass(g)/molar_mass(g/mol) PS : don't forget to convert T=50 celcius to Kelvin.