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This phrase from your post
"the circle surrounding the pool is the deck"
is incorrect.
A correct version is
"the ring surrounding the pool is the deck."
To answer first question, you should subtract the area of the smaller circle from the area of the greater circle.
Do you see the difference ?
To your second question, the answer is "Yes".
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As I see from your post, you treat words ( terms ! ) very carelessly.
Be more accurate with it ( ! )