direct proportion of a question

Question

A milk man mixes 2 litres of water in 11 liters  of milk. what is the amount of milk required if he wants to add 13 liters of water to it

Answer 1

2 litres of water --> 11 litres of milk
1 litre of water --> 11/2 = 5.5 litres of milk
13 litres of water --> 5.5 * 13 = 71.5 litres of milk