There are several steps before you report the sale transaction..
You need to determine
1. your original basis. The basis on gifted property is the lesser of donor's basis and fair market value at the time of gifting - both are back in 1994.
2. adjusted basis by adding all improvement expenses paid during these years - do not add repair expenses that were deducted when paid in previous years.
3. accumulated depreciation for years the property was rented. Residential rentals are depreciated over 27.5 years - so I assume the basis was largely depreciated.
4. additional expenses paid to prepare the property for sale and sale expenses are added to the basis.
Then you report the sale transaction.
We need to be clear if you realized a gain on that sale.
If you do realize a gain - that gain will be taxable.
However - we need to verify if you correctly calculated the gain.
That is $48,000 (selling price) MINUS (adjusted basis)
The mortgage amount you might pay out of proceeds is not relevant.
To report the sale transaction - use form 4797 - report as separate items - the land and the building.
Use part I because you held the property more than a year
In part III - report that sale transaction as section 1250 property.
You mentioned - with $24,000. still owing me - please clarify if you provided financing ?
If yes - you might qualify for the installment reporting method.
Let me know if any additional details needed.