So is 4 floors / 10 seconds If you have 60 seconds you can multiple 10 by 6 because 10×6=60 so you also have to multiple 4 by 6 4×6=24 and because it's descending it's 100-24= 76
It would be at the 76th floor because 10 seconds times 6 seconds is equivalent to 60 seconds. So you would also multiply the 4 floors by 6 to get 24. You would finally subtract 100 an 24 to get the 76th floor. Hopes this makes sense, and I hoped this helped!