GVIM : how to make a gui setting "permanent" via ( /root/.vimrc )?

GVIM : how to make a gui setting "permanent" via ( /root/.vimrc )?

Dear Sir/Madam, Soon as you open GVIM you can go to..
Edit --> Select Font
and then select something like.. "12" px instead of the default 10px.
this setting is not permanent unless it goes into
/root/.vimrc
file ( i login as root to my linux ).
the question is, how do i find the "line" that goes into
/root/.vimrc
?