So basically, he wants to make mixture where lemon=lime
it is 6 gallons so 40% of 6=0.4 times 60=2.4=lemon 60% of 6=0.6 times 60=3.6=lime so to make them equal 3.6-2.4=1.2 he must add 1.2 gallons of 100% lemon juice to make a mixture of 50% lemon and 50% lime
