How many units of Botox would I need for horizontal wrinkle between eyes? (Photo)

Every time I research Wrinkles between the eyes I find: "frown lines" "bunny lines" "the 11s " but most of them are talking about the vertical lines. I rarely see pics of people with the horizontal one. what is the wrinkle that's horizontal right in between my eyes at the very top of my nose? I really don't have any other wrinkles besides that one so why is that? Does it mean it's there bc I frown all the time or something? & approximately how many units of Botox am I looking at here? Thanks