Answer: 34 people in each row
Explanation:
4 people are holding flags. You don't say if they are part of the 30 people or 4 additional people. I'll assume they are additional people not included in the 30 people in rows. So the total number of folks in the marching band is:
(30 people in rows) + (4 additional people holding flags) = 34 people in the band.