5c + 3 a =25 c is the cost of children ticket and a is the cost for adult tickets.
4c +4a =28
Now multiply first equation by 4 and the second equation by 5
20c +12a =100
20c +20a = 140
Now subtract equation 2 from 1 we have -8a =-40 a = 5
Now substitute the value of a in equation 1 5c =25-15 c= 10/5 =2
children's ticket cost $2