[填空题]
A hot-air balloon achsidq,.,bchx8g /s 1 djjs-c- sieve7u:r6i6xjndw wkq-* p xhc ;i,s its buoyant lift by heating the air inside the balloon, which makes it less dense than the air outside. Suppose thu*pd qjx 6w iinkx6-r7,hw:;ce 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)
