Let's start by understanding the given information. We have a mixture of 45 liters that contains milk and water in the ratio of 7:3. We need to add some water to this mixture to change the ratio of milk and water to 3:7. We need to find out how much water should be added.


To solve this problem, we can follow these steps:

1. Calculate the amount of milk and water in the initial mixture.
2. Calculate the ratio of milk and water in the initial mixture.
3. Calculate the amount of milk and water in the final mixture.
4. Calculate the ratio of milk and water in the final mixture.
5. Find the difference in the amounts of water between the initial and final mixtures.
6. Add the required amount of water to the initial mixture.


Given that the initial mixture contains milk and water in the ratio 7:3 and the total volume is 45 liters, we can calculate the amount of milk and water as follows:

Amount of milk = (7/10) * 45 = 31.5 liters
Amount of water = (3/10) * 45 = 13.5 liters


The ratio of milk and water in the initial mixture is 31.5:13.5, which can be simplified to 7:3.


We want the final mixture to have a ratio of milk and water as 3:7. Let's assume that we need to add 'x' liters of water to the initial mixture. The amount of milk in the final mixture remains the same as the initial mixture, i.e., 31.5 liters. The amount of water in the final mixture will be (13.5 + x) liters.


The ratio of milk and water in the final mixture is 31.5:(13.5 + x).


To change the ratio of milk and water from 7:3 to 3:7, we need to add enough water to make the amount of water 7 times the amount of milk in the final mixture.

Difference in the amounts of water = 7 * amount of milk - amount of water
= 7 * 31.5 - 13.5
= 220.5 - 13.5
= 207 liters


To achieve the desired ratio, we need to add 207 liters of water to the initial mixture.

Therefore, the answer is option A) 60 liters.