What’s the function value when x=-1

Adam is building a deck in his backyard around a tree. the deck is in the shape of a regular octagon. in the center of the deck, there is a hole for the tree. if a = 10.9 ft, s = 9 ft, and the diameter of the hole is equal to 7 ft, find the area of the deck to the nearest tenth of a square foot. (use 3.14 as an approximation of pi.)