SBI PO 21 June 2015 Paper

In a 140 litres of mixture of milk and water, precentage of water is only 30%. The milkman gave 20 litres of this mixture to a customer. Then he added equal quantities of pure milk and water to the remaining mixture. As a result the respective ratio of milk and water in the mixture became 2 : 1. What was the quantity of milk added ? (in litres)