please answer it in detailed solution. thank you

A methane-nitrogen mixture of fuel gas (96% methane) is burned with 40% excess air in a continuous water heater. Both fuel gas and air enter dry at 25C. Water is heated at a rate of 35 kg/s from 25C to its normal boiling point without vaporization. The flue gases leave the heater at 210C. Of the entering methane, only 80% burns to carbon dioxide and the rest burns to carbon monoxide. What volumetric flow rate of fuel gas (in liters/second) is required if there are no heat losses to the surroundings? D