The O'Brien's are building a rectangular deck around the outside of their circular pool.
a.) Find the combined area if the deck is (2x + 3) units wide by (5x + 6) units long. Show all work.
b.) Find the area of the pool only if it is (x + 5) units across. Show all work.
c.) How much lumber should the O'Brien's buy in order to build their deck? Use mathematics to justify your answer.