The gas that undergoes combustion produces 2428 J of heat, which implies that
Likewise, work done by the system means that work was performed by the gas on the surroundings, which once again implies a minus sign.
Because the gas burns at constant pressure, the heat given off will also be the enthalpy change,
Convert J to kJ to get
Since you're dealing with 1 mole, you can write
Now use this equation to determine
SIDE NOTE I'll leave the rounding to the correct number of sig figs to you.