Answer-How many boxes are there between N and R?

Only two boxes are placed above box P. Only one box is placed between box S and P. Three boxes are placed between box N and O. N is placed above O. As many as boxes are placed between box S and Q as between box Q and M. Clearly, we cant place S, Q and M fulfilling the given condition in Case 2. However, in Case 1 we get the arrangement as follows Evidently, R will be filling the vacant position in Case 1.