I need some help getting a property value

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I know how to estimate property value based on comparable sales. The house I'm going to today is a little different from what I've seen. It was built in 1950 and is a 4/2 bath, It was originally a 2/1 and the owners added on 2 more bedrooms, 1 bath and a kitchen. So it's basically two 2/1 living areas, both with kitchens. The current owner is living in the front section and they rent out the back rooms for $450 each, the tenants share the kitchen and common areas.

It generates $900 in rental income as a room rental, but could also be rented as a 2/1. Do I comp it as a 4/2 even though it has two living areas? It is not a duplex per se, but can be treated as one. As a 4/2 it comps at $80,000, so it's a great investment property. I need a little help, Thanks