Can you please help me with this physics question

It is already old, but still remains unsolved

The Archimed's force, that gives cause to buoyancy, is B=d.V.a, where:

B is the vertical up force
d is the density of the fluid
V is the submersed volume
a is the local gravity acceleration

as the baloon stays in equilibrium, not moving up or down, B=ma, so we have

total mass = helium mass + baloon mass + yogurt mass

helium mass = 0.2 x V

(0.2V+0.01+0.1)x 10^-5=1.2 x V x 10^-5
0.11+0.2V=1.2 V
V=0.11m³