Answer: 11 cups
Explanation:
Given : A recipe for fruit punch calls for 2 cups of pineapple juice for every 3 cups of orange juice.
Let x be the number of cups of pineapple juice would be needed for 16.5 cups of orange juice.
Since the quantity of pineapple juice is proportional to the quantity of orange juice to make fruit punch , so we have the following equation:-

Hence, the 11 cups of pineapple would be needed.