Answer: The cost of child's ticket = $10
The cost of adult ticket = $ 13
Step-by-step explanation:
Let x be the cost of a child ticket and y be the cost of an adult ticket.
Then According to the question, we have

Multiply equation (1) by 3 and equation (2) by 2, then we have

Subtract equation (1) from equation (2), we have

Substitute the value of x in equation (1), we get

Hence, the cost of child's ticket = $10
The cost of adult ticket = $ 13