What to do with first rental property that is almost paid off?

[Holly Hair]

WE have our first rental property that is four years from being completely paid off. (About $20,000 left).  We have about $100,000 cash and we’re itching to make real estate be new streams of income for us in retirement.  Do we go ahead and pay off this rental?  This property is a two bedroom near a major university and has increased in value in the past five years over 100%  We also put a new roof on it two years ago, along with a new AC.  We are just learning and don’t want to make stupid mistakes!  Thanks for your advice