I'm assuming you meant 2/3. I have the same problem, and I'm not 100% sure why, but I checked it and it is correct.
I know BIM says it is incorrect, but the answer while doing it several ways is 21. I'm sorry this wasn't more helpful.
You must scuba dive to the entrance of your room at Jules' Undersea Lodge in Key Largo, Florida. The diver is 1 foot deeper than 23 of the elevation of the entrance. What is the elevation of the entrance?
2 answers
Oh! You just have to say it is -21 feet, because it is below sea level. Hope this helps. BIM took that answer, so yeah.