Apparently it's 35 ft.
This is what I learnt the on my second reading of Choose Your Own Adventure. This time I decided to make some careless decisions which led to a far worse ending although I did meet an archaeologist called Dr. Dudley Crake who fell into the bottomless pit found a 19 century Japanese sword NOT the coverted silver sword. It ends with the sword becoming property of the state and us all going for dinner- although I haven't found out what we eat.
This reading was a lot less satisfactory than the first.