Let be "x" the cost in dollars of an adult ticket and "y" the cost in dollars of a child ticket.
You know that a 5 adults and 4 children went to the museum and the total cost was $19. Therefore, you can write the following equation:

The word "Three times" indicates a multiplication by 3. Therefore, "The
adult admission fee is three times the fee for a child" can be written as:

In order to find the values of "x" and "y", substitute the second equation into the first one and solve for "y":

To find "x", substitute the value of "y" into the second equation. Then:

Therefore, you can identify that the correct options are:
- One of the equations to be used in solving the problem is :

- The adult fee is 3 dollars.