If a tank holds 52 l of water. How much water is in the tank when it is 3 by 4 full?

The tank holds 52 L of water.

So, if the tank is 3/4 full, it would contain 3/4 of the maximum amount of water it can hold.

Thus, amount of water when it is 3/4 full = 3/4 x 52 = 156/4 = 39 L.

Therefore, there are 39 L of water in the tank when it is 3/4 full.