Please Show Work on how you determined the answer

Consider the basic technique that you were taught for subtracting large integers "by hand" in grade school. What would be the worst-case complexity for subtracting one N-digit number from another and for subtracting 1 from an N-digit number?(choose 1 answer below)

		O(1); O(1)
		O(1); O(N)
		O(N); O(1)
		O(N); O(N)
		O(N 2); O(N)
		none of the above