Methane (ch4) at 25c, 1 atm enters a furnace operating at steady state and burns completely with 140% of theoretical air entering at 400 k, 1 atm. the products of combustion exit at 700 k, 1 atm. kinetic and potential energy effects are negligible. if the rate of heat transfer from the furnace to the surroundings is 400 kw, determine the mass flow rate of methane, in kg/s.