I think in this case that working directly with base 10 numbers is going to be more effective than base 5, so please do these using the base 10 blocks or other base 10 manipulatives.

First try it yourself	then watch my demo of one way to do it
638 divided into 5 sets	video
638 divided into sets of 5	video
638 divided into 21 sets:	video
638 divided into sets of 21	video

I'm going to ask you to write about which way of thinking about division made the problems easier for you, so make sure you are thinking about the appropriate division model when you are working these.