80% of 20 is 16, because 80% is 4/5 and 20 divided by 5 is 4, multiplied by 4 is 16. Area is L x W, so 16 times 20 is 320, and don't forget unit of measurement, ft^2 for area
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
