At a theme park, it costs for entrance :-
7 pounds for an adult and 4 pounds for a child.
The car park costs 3 pounds for a car.
The car park costs 5 pounds for a minibus.
The car park costs 8 pounds for a coach.
A group of 3 adults and some children went in a minibus.
It cost them 58 pounds to park and go inside.
How many children were there?