I bought 146 acres for $105K in 1998, divided the land in (4) 35 acre parcels. Currently, one of 35's is under contract for $117K. Will I have to pay capital gains?

I bought 146 acres for $105,000 in 1998.  In CO where I live, 35 acres or more, can easily legally be divided.  I mapped the land in four 35 acre parcels. I was married then built a house on one of the parcels.  In 2015, I got divorced and sold the house (because i couldn't keep it up by myself) along with one of the 35's acres (so the new owners bought 70+ acres). The funds from the sale of the house/land were split between us, and I put mine into purchasing a condo for my 2 daughters and me. 

Through the divorce I got the remaining 70+ acres. I now have one of 35's under contract for $117K.  I am single head of household for me & my daughters, and i make under $50K annually. If it sells, will I have to pay capital gains?  

If the second parcel sells for likely about $115K - $120K (it is also listed and there has been interest), will I have to pay capital gains on that?  Just trying to figure out tax implications before the end of the year.  

Your help and advice is much appreciated.  Thank you!!!