Adding a comma after a field

[LG]

If i am using =([F_Name] + " ") & [L_Name] this in a text box how would I be
able to add a comma after the L_name when it addresses the member?
Ex currently the above produces John Smith I would like it to have the
result of John Smith,
Thank you

 

[Jerry Whittle]

=[F_Name] & " " & [L_Name] & ","

I avoid using the + sign to join fields as it can get confusing if numbers
are involved.