Only 25 and 28 are functions.
A function must have only one y value per x value. For 26, the y value of 0 and multiple others have two different y values. For 27, all x values less than 0 have multiple y values.
Answer:

We also know that for Wedneday we have two times tickets for adults compared to child so we have

And using this condition we have:

And solving for X we got:

So then the number of tickets sold for child are 36
Step-by-step explanation:
For this problem we can set upt the following notation
X = number of tickets for child
Y= number of tickets for adults
And we know that the total revenue for Wednesday was 831.60. So then we can set up the following equation for the total revenue

We also know that for Wedneday we have two times tickets for adults compared to child so we have

And using this condition we have:

And solving for X we got:

So then the number of tickets sold for child are 36
(x + y = 125)3
5x - 3y = 41
3x - 3y = 375
8x = 416, x = 52
52 + y = 125, y = 73
Solution: the numbers are 52 and 73