Which one

I am looking at the Leupold Mark Ar scope for my new BCM 18" build. If I am wanted to be able to reach out 400 yds what kind of magnification should I be using?

The 3x9 or the 4x12 $349 for the 3x9 and $499 for the 4x12 on opticsplanet.com

opticsplanet.com is pricey, you can do better by around $50 with a little shopping.
I use a Leupold 4.5-14 on my varmint upper which is more than enough scope on varmints out to 350 yards.
Need more info on what you plan to use it for

Let’s just say I wanna be able to hit a soda can doing my part to obviously

4-12x.