Balloons are often filled with helium gas because it weighs only about one-seventh of what air weighs

Question:

Balloons are often filled with helium gas because it weighs only about one-seventh of what air weighs under identical conditions. The buoyancy force, which can be expressed as Fb = paiv gV balloon, will push the balloon upward. If the balloon has a diameter of 10 m and carries two people, 70 kg each, determine the acceleration of the balloon when it is first released. Assume the density of air is r = 1.16 kg/m3, and neglect the weight of the ropes and the cage

Balloons are often filled with helium