Formulas for multifamily deals

[Account Closed]

My husband and I are just getting our toes wet but we determined to find our way to financial freedom.  We would like to invest in multifamily units and there are a few locations we are interested in that have multifamily units for sale (8 or more units).  For the more seasoned investors, is there a formula that you use to determine what is or is not a good deal?  

An example: 6 unit town homes.  The structure is under 5 years old.  Rent is $700 per unit (each unit 2 br 1.5 bath).  Owner pays water, sewer, garbage.  The asking price is $620K.  The rent is appropriate for the area.  Why is this or is this not a good deal?  

Thank you