The volume of the hot air balloon is 490 cubic meters, and the outside air density is 1.244kg/m3, so the buoyancy is 609.56g, and g is the acceleration of gravity.

There is 220kg in the hot air balloon, so the air in the hot air balloon can only float when it weighs at most 389.56kg, so the internal air density is 0.795kg/m3.

Therefore, according to PV=nRT, the internal and external air pressures are equal, so the density is inversely proportional to the temperature, so the internal temperature is [(273+10) *1.244/0.795]-273 =170 degrees Celsius.