Lay out the weekdays for a 31-day month starting on Wednesday:
W, Th, F, Sa, Su, M, Tu, W, Th, F, Sa, Su, M, Tu, W, Th, F, Sa, Su, M, Tu, W, Th, F, Sa, Su, M, Tu, W, Th, F.
Sundays fall on days 5, 12, 19, 26 (four Sundays). Saturdays fall on 4, 11, 18, 25; only the second Saturday is a holiday, i.e., day 11.
Total holidays $= 4$ (Sundays) $+ 1$ (second Saturday) $= 5$.
Working days $=31-5=26$.