How many liters of water should be added to 18 l of a 14% bleach solution to the remaining solution contains only 10% bleach

14% * 18 L = 2.52 L of bleach are in the container. In order for that to be 10% of the contents of the container, there must be 10*2.52 L = 25.2 L of solution in the container.

Then 25.2 -18 = 7.2 liters of water must be added.