Help with Sell of Rental Property - When the market had gone down, we held on to our property and rented it. We just sold it in 2015. How do we figure Capital Gains?

We purchased the home in 2003 and tried to sell in 2007.  The market crashed and we held on to it as a rental.  The rent covered the mortgage, so we never made in income on it.  We sold the home in 2016.  Unfortunately, it looks like we have to pay capitial gains on it.  How do we figure out the portion of the capital gain that we have to pay taxes on?

I don't know if this could help us.  We have moved out the home we sold to our new home to take care of my elderly parents.  When the market crashed, we were not able to sell and converted it to a rental so we would loose the house.

Thanks.