This question seems to me to be an open question. I think it's difficult to say without context. If "going" suggests some ongoing action then how can it be said to have been finished or even "has been done"?
Alternatively, the scenario might be in a classroom of students doing a test, and that you have completed your test and patiently waiting for the teacher to take your test paper and asks " How's everything going?" Its not a direct question, and the idea is implied. You can answer either a or b.
So, they are either both correct or both incorrect answers.