Question

A gaseous fuel mixture stored at 745 mmHg and 298 K contains only methane(CH4) and propane (C3H8). When 12.8 L of this fuel mixture burns, it produces 775 kJ of heat. The enthalpy of combustion for CH4(g) is −802.5kJ. The enthalpy of combustion for C3H8(g) is −2043.9kJ​

What is the mole fraction of methane in the mixture? (Assume that the water produced by the combustion is in the gaseous state.)​