To find the answer, we will have to find the percentage of $273 to $ 3500, and we can use the formula:

In this case:
273/3500 x 100%
=39/500 x 100%
=7.8%
Therefore the annual interest rate would be 7.8%.
Hope it helps!
So what you are trying to find is the certain amount of children tickets and adult tickets. the final amount is a total of $12. This means that a unknown number of children tickets (c) times 1.50 (price of each ticket for children) plus the unknown number of adult tickets (a) times 4.00 (price of each ticket for adults) equals a final cost of $12.00.
Equation: 1.50c+4.00a= 12.00