A chemist has three different acid solutions.
The first solution contains 15 % acid, the second contains 30 % acid, and the third contains 50 %
acid,
She created 78 liters of a 35 % acid mixture, using all three solutions. The number of liters of 50 %
solution used is 3 times the number of liters of 30 % solution used.
How many liters of each solution was used?