Calculate the gross and net heating value (kJ/m at STP) of a fuel gas analysing 80% methane, 10% ethane, 6% propane and 4% butane. The standard heats of combustion are -890.4, -1559.9, 2220,-2878.52 kJ/mol respectively for methane, ethane, propane and butane. The latent heat of vaporization of water at 298K is 44.014 kJ/mol.