Answer is E. 64
Step by step
You have 5 cup recipe that’s made of 2c lemon juice
You want to make 10 gallons, let’s change it to cups
10 gallons x 16 cups per gallon = 160 cups
160 cups divided by the 5 cup recipe = 32 recipe portions
32 recipe portions x 2 cups lemon juice = 64 cups lemon juice