Here, agmsy is one elementary product. Similarly, agmtx, fbmsy are elementary products as they contain exactly one entry from each row and each column. So, We can say that for any n x n matrix there will be elementary products.
Elementry product will have 5 elements. For first element we have 5 choices (any of the elements from first column) then for second element we have 4 choices (we can't take the value from the row that first element of the product comes) and so on. Hence,