Tickets are 24$ for 1 adult.
Two thirds of 24 will be the price of 1 child. Divide 24 by 3 and you get 8. Since 8 is 1/3 of 24, 16 would be 2/3 of 24.
So the price for 1 child is 16$.
2 adults and 2 children is 24+24+16+16
The family had to pay a total of $80