Upthrust force = Weight of the displace liquid
Total upward force = downward force

Force of viscosity +upthrust force = weight of metal sphere

6πμrv + weight of the displaces liquid = weight of the metal sphere

6πμrv + mass of the displace liquid ×g = [ mass of the metal sphere × g ]

6πμrv + volume of the displace liquid ×Density of the liquid × g = volume of the metal sphere × density of the metal sphere × g

μ ⟹ Viscosity of the liquid
r ⟹ radius of the metal sphere
g ⟹ Acceleration due to gravity
ball ⟹ Density of the metal sphere
l ⟹ density of the liquid
v ⟹ Terminal Velocity