The Mass of a Hot-Air Balloon and Its Cargo (Not $\degree$

The mass of a hot-air balloon and its cargo (not including the air inside) is 250 kg. The air outside is at a temperature of 10 $\degree$ C and a pressure of 1 atm = 10⁵ N/m². The volume of the balloon is 400 m³. Which temperature below of the air in the balloon will allow the balloon to just lift off? (Air density at 10 $\degree$ C is 1.25 kg/m³.)

A) 37 $\degree$ C
B) 293 $\degree$ C
C) 99 $\degree$ C
D) 200 $\degree$ C