If a cup is a regular sized cup that is 2 deciliters, and 1 liter equals 10 deciliters, that means that 1 liter = 5 cups, which means that 3 liters = 15 cups. If it is a cup that has 0.33 dl, then the correct number would be 9 cups.
Ooh so the directions tell us what we need to find the entire line, which is made up of FH. so just add GH (15) and FG (6) together to find FH. so that is 21. FH=21.