Briefly:

The correct formula is:

27 - 2 = 25


That is the hop pocketed $2 from the $27 paid for the room. Leaving the manager with $25.


27 + 2 is inappropriate

That would describe the situation where instead of pocketing $2, the hop curiously donated another $2 on top of that paid to the manager.

---

For the record I did work that out from scratch, even though I had a vague recollection of where to find the answer on the Internet.