We have two fractions and are being asked to subtract them.
7/8 and 1/3 don't have the same denominator, so to do as so, we need to find the LCM of both denominators, multiply them to that, and do the same for the numerators.
So what is the LCM (Least Common Multiple) of 8 and 3?
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.