Grape juice is 100% fruit juice so for 9 liters of grape juice you have 9 liters of fruit juice
9 liters fruit juice
9 liters juice
for every liter you add of fruit punch, you get .35 liters of fruit juice. so the question is how many liters of punch (we'll say x liters) do you have to add to get the ratio of fruit juice to total juice to be 74 to 100?
9 liters of fruit juice + 0.35x = 74
9 liters of juice + x 100
cross multiply
(9 + 0.35x) 100 = (9 + x)74
900 + 35x = 666+ 74x
234 = 39x
x=6 liters of brand A fruit punch