The correct option is C = 7 + 2n. From the question given above, we are told that, a notebook costs $7 and divider cost $2 per kg. So if you buy one notebook, it will cost $7 and if you buy n packages of dividers, it will cost $2 * n = 2n. If you add all the costs of the items together, you will have Cost [C] = 7 + 2n.
