Question 1163687
For n distinct objects distributed into r distinct boxes (where order within the box does not matter, and a box may be left empty):  {{{ r^n }}}<br>

The reasoning is as follows: for the four balls labeled A,B,C,D and four boxes labeled w,x,y,z,   you have 4 places (w,x,y,z) to put A, times (4 places to put B), times (4 places to put C), times (4 places to put D).