insert leading or trailing spaces

Hi all,
Anyone can advise on the formula to add trailing or leading spaces?
1. Add trailing spaces:
When I enter 12345, excel must be able to append 16 spaces behind as field length is 21 characters

2. Add leading spaces
When I enter 12345, excel must be able to append 16 spaces in front as field length is 21 characters

Hi there any help is greatly appreciated as I am still searching for a solution