Hexagon radius = side = r =9 ft.
Hexagon Area = (3√3)/2 * r²
∴ Area = (3√3)/2 * 9² ≈ 210.444 ft²
The cost for the carpet and installation is $3.75/ft²
∴ The total cost = Area * cost per ft²
                         = 210.444 * 3.75
                         = $ 789.166