Use discrete fine rates to choose the feasible solution

Ace borrowed 10 books and 3 audio-visual items. Overdue fines per day are $x$ cents per book and $y$ cents per audio-visual item, each a multiple of 5 cents. Four days after the due date, he realises at school that none has been returned. He has $k$ books and no audio-visual items with him.

Option A: Return these $k$ books on his way home and the remaining books and audio-visual items the following day; total fine $14.55.

Option B: Return all items the following day; total fine $15.

Using this information, find $x$ and $y$.