No matter what number you pick, when you subtract the two digits, you end up with a multiple of nine.
18-1-8 = 9
12-1-2 = 9
54-5-4 = 45
99-9-9 = 81
It won't matter which two digit number you chose.
You will find that *all* the gifts that are the same as your gift are multiples of 9.