A porter moves along a straight railway platform whose origin is chosen at the middle of the platform. His successive displacements, in the order shown below, are all measured with respect to this origin and along the +x direction towards one end.
(i) Write an algebraic equation in d representing the above situation and hence find the value of d.
(ii) Calculate the total distance walked by the porter in the whole trip.
(iii) If the porter had instead wanted to reach the origin after the fourth move, what would the value of d be? Also compute the corresponding total distance in that case.