In order to put this problem into an algebraic equation it can be written as 5L*(.25) + XL*(.35) = (X+5)*(.34)
The reason we multiply 5 by .25 is to get the percentage of acid that is present in the solution.
X * .35 represents the X amount of acid that is in the 35% solution.
In order to find the total amount of acid in the solution we have to add them both together.
Since it is the total amount of acid in solution we have to remember that not just acid is being added, solution is also being added. That is why on the right, (X + 5) is written.
(X+5) represents the total amount of solution (acid included).
Finally we multiply the (X+5) because we want to reach a solution of 34% acid.
So just solve for X.
x(.35) = X(.34) + 5(.34) - 5(.25)
X(.35) - X(.34) = 5(.34) - 5(.25)
X(.35 - .34) = 5(.34 - .25)
X(.01) = 5(.09)
X = 45 liters