I got the first one but i’m stuck on the other 3, someone please help!

         2, 1,3

Step-by-step explanation:

The answer is 4 liters.

Step-by-step explanation:

We want a final 25% solution, which means that the solvent should constitute 25 percent of all the liters of solution.

Let us call the litres of 40% solution, so when they are added to the 12 litres of 20% solution, the total litres of the new solution are:

of these liters, 25% must be the solvent:

Now for the 40% solution, the liters of the solvent are , and for the 20% liter solution, the liters of solve are liters. Thus the total liters of the solvent are

Therefore