Escape Game - Hotel

Am stuck at the green elevator door there needs to be more clues I even watched the adds for a clue hint an the answer they both say the same thing calculate the number between 1 and 7 on the elevator panel as a hint an the answer hint don’t give you the answer that where am stuck at

Not terribly hard but loads of puzzles. I did need one hint - I didn’t see the dark spot where I was to use the cloth.