sin(∠ACB) = 4/8 = 1/2 therefore ∠ACB = 30° Therefore since ∠BCO = 90°, ∠ACO = 60° Therefore ΔOAC is an equilateral triangle because the two radii, OA and OC are equal, making it isosceles, and it has one 60° angle. So all the sides of ΔOAC are equal, so OC=8. So the radius of the wheel is 8, its diameter is 16 and its area is pr² = p(8)² = 64p. Edwin