Sarah is in a basket hanging from a balloon filled with helium.
M = mass of basket, Sarah, and empty balloon
ρHe = density of helium gas at 27˚ C and 1 atm
ρair = density of air at 27˚ C and 1 atm
To what volume should the balloon be filled to achieve neutral buoyancy? (Ignore the volume of Sarah, but include the weight of the helium.)