One final piece of help:-
The question you have posted here looks like it has come from a website (or some “application”) where you are required to “Enter” your answers into the boxes provided and only the “correct” (expected) answers will be accepted.
If that’s the case, then in part c) the answer you first come up with may well not be accepted in the box(es).
I suspect (though I may be wrong, ofc) that the answer in the first box of part c) may need to be”3” though we will expect you to be able to demonstrate how that is arrived at.