LP gas burns according to the following exothermic reaction: C3H8+5O2--->3CO2+4H2O?

What mass of LP gas is necessary to heat 1.8 L of water from room temperature (25.0 C) to boiling (100.0 C)? Assume that during heating, 15% of the heat emitted by the LP gas combustion goes to heat the water. The rest is lost as heat to the surroundings. Change in enthalpy= -2044 kJ