Unix/Linux commands help

12) What command opens a line below the cursor? 13) In what mode must you be to enter text into the file? 14) What command tells the editor to take you back to command mode from append mode? 15) What command do you type to leave vi without saving the changes to a file? 16) What command instructs vi to save changes and return you to the shell? 17) In what mode must you be to save the changes you made into the file and quit the editor