If the scale says 1/2 inch is equal to a foot then you can divide 9 by 1/2 to get 18. The units would then change to feet so this is one portion of the real dimensions of the deck. You would then do the same for 16 inches and the other dimension would be 32 feet.
The dimensions for the real deck are 18 feet by 32 feet.
I hope this helps you :D
