Question

If the fuel he carries produces 36 kJ of heat per gram when it burns, how much fuel should he carry? (For the sake of simplicity, assume that the transfer of heat is 100 % efficient.)

Answer 1

He must carry enough fuel to provide the heat energy he NEEDS.

That is, 1 gram of fuel for every 36 kJ of heat energy he NEEDS.

In the form of an algebraic equation . . .

Fuel to carry (grams) = (total heat energy he's going to NEED) / (36 kJ) .

Sadly, the question gives no hint of how much heat he's going to NEED.