You should get (or have gotten) a tax reporting statement, such as a 1099-S or a K-1 from the estate (which would have filed or will file a Form 1041).
Regardless, the calculation typically involves subtracting your basis (the fair market value on the date of your mother's death) from the selling price. If the sale occurs shortly after death, there is usually little or no gain and, if the property is not used by a beneficiary or family member, possibly a small loss due to selling expenses.
Check with the estate administrator or the probate attorney.
