Does the 3 company lines have to go in line 12-15?

>How can I know the user 'how many lines he input' ?
>
>i got a rich textbox for the user to input.
>E.g when he input 10 lines and press"confirm" button.
>then I need to put three "company rules" in 12th-15th lines (automically)
>How can i do that??