Thermodynamics Question

A hot-air balloon achieves its buoyant lift by heating the air inside the balloon, which makes it less dense than the air outside. Suppose the volume of a balloon is 1800 m³ and the required lift is 3300 N (rough estimate of the weight of the equipment and passenger). Calculate the temperature of the air inside the balloon which will produce the required lift. Assume the outside air is an ideal gas at 0°C. What factors limit the maximum altitude attainable by this method for a given load?