Answer:
500 kg
Explanation:
If 17000 N hot air weight displaces 25000 N cold air weight, then the difference of 25000 - 17000 = 8000 N in weight would result in the buoyant force that lift the whole system.
If g = 10m/s2 then the total mass that it can lift (including the 300kg basket) is
8000 / 10 = 800 kg
So the maximum additional load that the balloon is able to lift is
800 - 300 = 500 kg