In Figure B3, a sports ground is designed to have a running track. The running track is formed by the shape of a rectangle with two semicircles on both sides. Given that the length of the running track is 400 m, the radius of the semicircle is r m, the length of the rectangle is x m. X Figure B3 (a) Express (1) the area A, of the sports ground, in term of x and ; (ii) the length L, of the running track, in term of x and r ; and (iii) the area A, of the sports ground, in term of r only (b) Find the maximum area of the sport grounds