Write a method that accepts two magnitudes for possible motion along a line. Return a string representing the possible ending locations, starting from zero, and either adding or subtracting each magnitude. The string must list the possible results in increasing order. For example, with magnitudes of 3 and 7, the returned string would be: "-10, -4, 4, 10". Please note that magnitudes are never negative, but could be zero. Also note that you should always return a string with four numbers, even if they are all the same in some cases.