In a mixture, the ratio of milk and water is 5 ∶ 4. If 20 liters of mixture is taken out and 10 liters of water is added to the mixture, such that the ratio of milk and water becomes 5 ∶ 6. What is the initial concentration of the mixture at the beginning?
1
45 liters
2
54 liters
3
65 liters
4
78 liters