The heat released by cpmolete the combustion of organic products with oxygen is called heat of combustion.
Here 1 mol of CH4 realesed 802.3 KJ
To emit 264 kJ you multiply you need (1 mol of CH4/802.3 kJ)* 264 kJ = 0.329 mol of CH4
The molar mass, MM, of CH4 is 12 g/mol + 4*1g/mol = 16 g/mol
The to obtain the mass multiply the number of moles times the molar mass:
mass = n * MM = 0.329mol * 16g/mol = 5.26 grams
Answer: 5.26 grams