The bubble is moving with a constant velocity so the net force acting on the body is zero.
Stokes' law defines the drag force which is given by F=6πηrv
The buoyant force is given by B=Vρg=34πr3ρg
Hence, it can be written that
34πr3ρg=6πηrv⇒η=9v2r2ρg=9×0.35×10−22×(3×10−3)2×1750×10=10Pas