a The center of the hexagon and of the circle are the same point. Also length of one side of the hexagon = 90/6 = 15 units.
If we join each vertex of the hexagon to the center then we get 6 equilateral triangles (because internal angle of reg hexagon = 120 and vertex angles of the triangles = 60) so the radius = length of side of hexagon = 15 units (answer)
b Area = pi * 15^2 = 706.9 units^2 to nearest tenth. Answer