An X diagram can help you find the proportions of the components of the mix. This one tells you the ratio of 10% punch to 90% punch is 55/25 = 2.2. That means 20 gallons of 90% punch will require 2.2*20 = 44 gallons of 10% punch to make the desired mix.
44 gallons of 10% punch are needed.
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The numbers on the right in the diagram are the differences between the central number (the mix value) and the left numbers (the constituent values). Those number on the right give the relative proportions of the corresponding constituents. Here, the 90% punch to 10% punch ratio is 25:55 = 1 : 2.2.