Question 727848
Only 1 variable, call it c, the amount of volume in gallons of the 20% alcohol punch to add.


To clear the confusion, you want the ratio of the alcohol to the mixture to be 0.18, or 18%.
QuantityOfAlcohol/QuantityOfPunchMixture=0.18


{{{highlight((20c+15*2)/(c+2)=18)}}}
Solve for c.