In order to produce the number of mass of propane needed we have to follow the steps. First divide the heat needed by the enthalpy of combustion of propane which is -2220 kJ/mol. This time disregard the negative sign first.
2775 kJ /2220 kJ/mol = 1.25 moles propane
Next, obtain the mass of propane by multiplying the moles produced with the molar mass of propane which is 44.1 g/mol
1.25 mol x 44.1 g/mol = 55.125 grams of propane
55.13 grams of propane is needed in order to produce 2775 kJ of heat.