You can put this solution on YOUR website! If you divide 16 by 2 you get 8
--
If you divide 112 by 16 you get 7
--
If you divide 672 by 112 you get 6
--
If you divide 3360 by 672 you get 5
--
If you divide 13440 by 3360 you get 4
--
--
So you must multiply 13440 by 3 to get 40320