You need to find the mass of water in the pool.
Find the volume (10 x 4 x 3) = 120 m3
Water has a density of 1000g/m3,so 120 m3 = 120 x 1000 = 120 000 kg
[delta]H = 4.187 x 120 000 x 3.4 (and the units will be kJ)
You then use the heat of combustion knowing that each mole of methane
releases 891 kJ of heat so if you divide 891 into the previous answer,
you will get the number of moles of CH4
You need to know how much friction that object.
The answer is most likely A