Copy & Paste - copy current line. Paste after cursor - paste after cursor. Remove & Paster - remove current line - remove contents of line. undo - undo the contents of the line that has been removed. Use the Yank Buffer to save the contents were deleted.
Copy & Paste
'yy' - copy current line
'p' - paste after cursor
'u' - undo
'3yy' then 'p'
Remove & Paster
'dd' - remove current line
'p' - [N]dd uses the Yank Buffer to save the contents were deleted