[Related to Solved Problem 1.1 on page 8] Two students are discussing Solved Problem 1.1:

Joe: “I think the key additional information you need to know in deciding whether the doctor should keep the medical practice open 9 hours per day rather than 8 hours is the amount of profit she is currently making while being open 8 hours. Then she can compare the profit earned from being open 9 hours with the profit earned from being open 8 hours. This information is more important than the additional revenue and additional cost of being open 1 more hour.”

Jill: “Actually, Joe, knowing how much profits change when the medical practice stays open 1 more hour is exactly the same as knowing the additional revenue and the additional cost.”

Briefly evaluate their arguments.