How much pure acid should be mixed with 3 gallons of 20% acid to get 60% acid solution?

If mistaken you would cross multiply and divide tom find your answer which would be 9 gallons, because you would set up a proportion of

3 x

__ ___

20% 60%

so you would cross multiply 60 times 3 which would give you 180 and then divide it by 20 which will give you 9 gallons. I'm thinking.