A solution is 10% citric acid. if 3 liters of a 20% citric acid solution are added to it, the result is a solution this is in a ratio of 13 parts citric acid to 102 parts "other than citric acid". How many total liters were in the original solution (before 3 L were added)?

x = liters of original 10% citric acid.

3(20%) + x(10%) = liters citric acid

3 + x = total liters

(3(20%) + x(10%)) / (3 + x) = 13 / (102 + 13)

13(3 + x) = 115(3(20%) + x(10%))

39 + 13x = 115(3/5 + x/10)

39 + 13x = 23(3) + 11.5x

1.5x = 30

x = 300/15

x = 20 liters