How is the remaining portion of the *kitabah* debt calculated against the estate when the *kitabah* debt exceeds what is due from the estate's third?

Primary text

If the *kitabah* debt is considered and a portion remains outstanding, an alternative view suggests that the estate's wealth increases because the heirs receive a portion derived from the master's contract. If the remaining portion of the debt is one-third of the *kitabah* debt, the portion that must be considered against the estate is three-quarters of the *kitabah* debt, as one-quarter is due to the freed slave and thus not counted from the deceased's estate.