The first answer is A because (b+6) represents the sidewalk length. (With the pool length and the two corners, which equal 3 ft each.) Then, the sidewalk width would be (h+6) for the same reason. Multiply them and get the pool area plus the sidewalk area. But you only need the sidewalk area so you would subtract the pool area from the whole area, to get (b+6)(h+6)-bh, or A in the end.
Unfortunately, I do not know the answers to the rest of the problems. I still hope this helped though!
