We can solve the 3x3 problem by stacking all of the cups in the middle. On the 5x5 problem, we can solve it similarly by focusing on the corners than the center lines. Can you find a way to apply this to the 7x7 and 9x9 problems? (Hint: on the 9x9 problem, solving the corners will leave leftovers. How can you split the leftovers evenly to move to the center?
