I would say that they are different because if x - a has a value to the equation then that means a - x will not have the same value because it may be rearranged to a different equation but that doesn't mean that they will have the same value. that explain why x - a and a - x are not the same
Since theres 4 numbers and 60 spins if you divide it you get the average number that all the numbers would land on. 2 would be landed on 15 times if it went exactly to the calculations. not 100% sure though