move into rental or sell home

[Maru Interiano]

Help.  We are retiring in two years and plan on moving into duplex we own in Buffalo.  last week we put our primary home (living in for 7 years now)  and our former home we have rented for the last 7 years both homes in Lewis county ny where we work.  We thought let's put both up and see which sells first and move into the other.  We  received offers on both one for about 170,000 (rental) and our home for like 190,000.  How much would pay in capital gains selling the rental as apposed to our primary? Both were purchased for about the same price $67,000. our rental was purchased 25 years ago and our home about 7 yrs ago.  It would be easier selling the rental and our gross combined income is 78,000 joint per year and we owe 23,000 on one line of credit on our primary residents.