Break the 31 days into 4 complete 7-day weeks, 28 days, plus 3 leftover days. In a week where the Saturday is not a holiday, 6 of its 7 days are working days, only Sunday is off; this holds for 3 of the 4 weeks. In the one week containing the second Saturday, only 5 of its 7 days are working, since both Sunday and that Saturday are off. We can check each option by removing the 3 guaranteed-working leftover days and comparing what remains to this week-block total.
The four complete weeks contribute 23 working days, and the 3 leftover weekdays, all working days, add 3 more, giving 26 in total.
Therefore, the correct answer is 26.