There are few things to answer for this problem. First how many gallon of lemonade are left? You had 15 gallons and it's 60% gone. That means that 40% is left. You have to figure out how much 40% of 15 is. You do that by multiplying 15 x 0.40. The answer is 6.
Next, how much ice tea did you make? You figure this out with the ration 3:4 which can also be written as the fraction 3/4. The lemonade is the three and you know you made 15 gallons of that. 15 is 3 x 5. If you multiply the 4 times 5 also you will find out how much iced tea you made - 20 gallons.
How many gallons of iced tea are left? You figure this out by multiplying the percent left - 48% (100 - 52) by 20 gallons. 20 x 0.48 = 9.6 gallons.