[填空题]
A hot-air balloon achieves its buoyant lift by heating the ai w3p*gt mo +gx048kswvr insimgdg0 t,lp9*gf s3fc8de the balloon, which makes it less dense than the air outsideftd,c0f g*m 38g9pl gs. Suppose the volume of a balloon is 1800 $m^3$ and the required lift is 2700 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 that the outside air temperature is 0 $^{\circ} $ C and that air is an ideal gas under these conditions. What factors limit the maximum altitude attainable by this method for a given load? (Neglect variables like wind.) $\approx$ $^{\circ} $ C(Round to the nearest integer)
