Answer: 11c + 13d
Explanation:
its just adding by whatever variables are the same
16c - 5c is the same as saying 16 - 5 except of course they have a letter that you need to keep at the end.
so the answer would be 11c + 13d because the same rule applies to the other variables, try to keep it alphabetically organized, since I'm unsure if it is counted off if you don't.