Given the rationale, provide a reasonable question and answer. Step-by-step reasoning process: First find the total difference in weight between the two people: 60 pounds - 40 pounds = 20 pounds. Then divide the weight difference by the weight of each rock to find the number of rocks need to even the weights: 20 pounds / 4 pound / rock = 5 rocks.
 The question and answer:
Jack, who weighs 60 pounds, wants to play on the see-saw with his cousin Anna, who weighs 40 pounds. How many 4-pound rocks does Jack need to hold to make their weights equal?
The answer is 5