Milk is mixed with 18 part of water in a bottle, so that the mixture becomes 56 parts of the bottle. Amount of milk added is .
Bottle 1 contains a mixture of milk and water in 7:2 ratio and Bottle 2 contains a mixture of milk and water in 9:4 ratio. In what ratio of volumes should the liquids in Bottle 1 and Bottle 2 be combined to obtain a mixture of milk and water in 3:1 ratio?