RULE is: \[2\,\,1\,\,3={{2}^{2}}\,1\,\,{{3}^{2}}=4\,\,1\,\,9;3\,2\,2\] \[={{3}^{2}}\,2\,\,{{2}^{2}}=924;\] \[415={{4}^{2}}\,1\,\,{{5}^{2}}=16\,\,1\,\,25\] \[\THEREFORE \] \[2\,\,1\,\,5={{2}^{2}}\,1\,\,{{5}^{2}}=4\,\,1\,\,2\,5\]