i think we can sum the number of the visitors on the two days up: 6742+5487=12229.
so this many people visited.
now, if every 175th person gets a free ticket, we just need to divide this number by 175:
12 229/175=69 and
this means that
69 people got the free admission and that after that 154 more people came, so 20 people more and after than someone goes in for free!