I gave you the answer to number 11 on your other post, and for 12, this is how you do it...
10 ft 6 in is 10.5 ft first off.
Set up for cross multiplication... use 7^2 and 10.5^2 because it's area.
3/7^2 x y/10.5^2... 49y=330.75... y=6.75
So, 6.75 pints of stain are required to paint a deck 10 ft 6 in x 10 ft 6 in, if 3 pints is required for 7 ft x 7ft, and the amount of stain proportional to the area of the deck
