This needs to be solved with a system of equations.
1. define your variables. your variables can be anything you want, but I will use x and y. x=adult tickets; y=child tickets
2. Now, you need 2 equations. For the first equation you will use the facts you are given about money. Adult ticket costs 9 dollars, each child ticket costs 5 , and Mary spent $110. Make these facts into an equation using the variables you have defined
3. Now make an equation using the facts you are given about the number of tickets sold and bought. You don’t know how many of each ticket she bought, so you just use your variables to make an equation using the fact that Mary bought 14 tickets.
4. Now, you have two different equations. You can solve by substitution or elimination, either will work, however I prefer elimination. Put the equations on top of each other, and eliminate one of the variables. Find the value of the variable you did not eliminate, and substitute that into one of your original equations that you created in step 2 or 3. It doesn’t matter which one you substitute into. Now, you will have found the values of x and y. Remember, x is the number of adult tickets, and y is the number of child tickets.
I hope this helps!