[填空题]
A hot-air balloon achieves its buoyant lift by heatiz /d0*nzu,plpsr tc9 k +hg,r)ng the air inpzhi9hxqjs1.0i k.+r side the balloon, which makes it less dense than the air outside. Suppose the v. hsr.p0i+h iqz1j x9kolume 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)
