Under standard conditions, the density of air is 1.293 kg/m3 and that of helium is 0.178 kg/m3. A spherical helium balloon lifts a basket plus cargo of mass 277.0 kg. What must be the minimum diameter of the spherical balloon?

Answer 1

the balloon weighs 277*9.8 = 2714.6 N

add to that the weight of the helium enclosed. (volume * density * 9.8)

so, the volume of air displaced must weigh the same amount.

Now just plug in the numbers and crank it out.