It's interesting how you were able to solve this question with
alligation method. We don't know the resulting solution's weight, neither we do know the starting concentration for the solution to be mixed with 85% of 6-liter solution. Alligation is a method to find the amount of two ingredients which are mixed together to form a new mixture with the given amounts or concentrations in the pre-mixed solutions.
One viable method to tackle this question is to take into account 85% alcohol concentration of 6-liter solution for producing another solution with the concentration 90% by adding pure alcohol --> 5.1 + a = 5.4 +0.9a, where a is denoted for alcohol, a=3 (the same as sanju proposed).
Otherwise we could also consider 10% concentration required of non-alcohol concentration in the new solution and apply this to the present non-alcohol concentration 0.9 (6*15%). We should find when 0.9 liters of solution becomes 10%. This will occur when we have solution 9 liters. Hence we need to increase our solution by 3 liters (9-6).
yellowho wrote:A six-liter solution is 85% alcohol. How many liters of pure alcohol must be added to produce a solution that is 90% alcohol?
How do you do this without having to take 85% of 6 or allegation?
