I have attached an image showing a (what I believe to be) simple problem involving arranging four blocks, each of different dimensions. Yes, the blocks fit together perfectly in the first arrangement shown in the diagram when there are no gaps. I'm convinced that the solution is likely easily arrived at, but I am neither confident nor experienced in any in permutations and combinatorics in general. I believe that the answer is likely to come from the use of some sort of formula involving factorials and all that good stuff but I'm not entirely sure how. Can anyone give me an idea of where to begin? Or am I totally incorrect in approaching this problem as one involving combinatorics? Thank you very much for your help in advance.