Notice on the grid that all the items that have a number that is a multiple of 9 are the same item. That's because when you take any two digit number and subtract it by each of its digits, you will always get a multiple of nine. A few examples: 47 - 4 = 41 - 7 = 36 (4 x 9) 39 - 3 = 36 - 9 = 27 (3 x 9) 25 - 2 = 23 - 5 = 18 (2 x 9) Now you program it to put whatever Robin will say in any spot with a multiple of nine, and voila
it doesnt matter. whatever number you end up with from the math IS a multiple of nine. and all multiples of nine have the same answer. she isnt guessing the number you are thinking of she is guessing the object in the box.
This might help if anyone is still having trouble understanding this. No matter what two digit number you choose you'll end up with "Bunny Slippers" on the above grid.