A U-tube initially contains mercury with equal levels in both arms. A 20 cm column of water is gently poured into the left arm. Subsequently, immiscible oil of density 900kg m−3 is poured into the right arm until the mercury levels in the two arms become equal again.
(i) Calculate the height of the oil column added.
(ii) State the final difference, if any, between the upper surfaces of the water and the oil columns.