How Do I Figure Out ARV on a Duplex??

[Hayes Mercure]

Hey!

I'm looking at a duplex to BRRRR and am trying to figure out a potential ARV for it. It's actually a triplex, it has two 2br/1ba sides, then a 1br/1ba in the basement.

When looking at sale comps, I'm not sure what to look for. Would I add up all bedrooms(5) and bathrooms(3) and look at a single family home that's the same size? That doesn't seem logical to me, but have no idea. I can't find any duplex sale comps, unfortunately. 

And advice/suggestions would be highly appreciated. Thanks!