We don't know the value of 'a' nor the value of x, so we cannot evaluate further. This is the same as a^2*x because order of multiplication does not matter. For example, 2*3 = 6 and 3*2 = 6, so 2*3 = 3*2.
the distance from the top car to the bottom car is equal to the diameter of the wheel. The diameter is 40 m, and that is twice the radius. The radius of the Ferris wheel is (40 m)/2 = 20 m.
