Question 731016
Bad question.  No specification for the ratio of the alcohol to the acid in the 8 pints mixture, and you cannot expect to INCREASE the amount of alcohol from 20% to 30%.  If you want to accept this as an open-ended question, then you could pick any ratio between the alcohol and the acid that is possible.  


One way to approach is to make a total percent concentration rational equation and give one of the conditions that the volumes of each quantity of the available solutions must sum to 8 pints.  The thought is like this:

x for the alcohol volume, y for the acid volume,
{{{(20x+50y)/8=p}}} and {{{x+y=8}}}.  You would not care what the ratio is between x and y; only that you care that the value of p is 30, for 30%.  


According to that, you are back to a typical two component mixture problem without regard to the identity of the pure material in the available solutions or the resulting solution.


{{{(20x+50y)/8=30}}} and {{{x+y=8}}}
Solve for x and y.