Given that #DeltaH_"combustion"^@# for #"propane"# is #-2043*kJ*mol^-1#, what mass of propane is required to give #425*kJ#?
You have the equation; treat the energy as a product!
Normally, we would write the energy given as a negative quantity. Here, I have it listed as a reaction product (as indeed it is). Combustion of 1 mol propane gives 2043 kJ of energy. (That is 2043 kJ of energy are evolved per mole of reaction as written!)
So if 425 kJ of energy are evolved, then