|A) 1 litre paint||B) 1 litre water|
|C) ½ litre water and one litre paint||D) ½ litre paint and one litre water|
At the moment the paint is 3 liters of paint and 3 liters of water. We need to add to this to make the new ratio 2 liters paint to 1.5 liters water. As this is equivalent to 4 : 3 we can see that we have the right amount of water, and just need 1 liter of paint to make it correct.