Answer:
(170;120;60).
Explanation:
We know that:
Capacity of the theater: 350 people.
Adults is half the students.
Children's cost: $4.50
Student's cost: $7.50
Adults' cost: $12.50
Total Sales: $2415
We are gonna call x the children, y the students and z the adults:
So, the equation to express the capacity of the theater would be:

But,
(adults are have students)
So, the expression would be:

Solving y's and Isolating x :

Now, we need a expression for costs. We have:

Replacing the x and z equation:

Now, we solve for y:

But, we know that adults are half as many students, so:

Lastly,

Therefore, there are 170 children, 120 students and 60 adults. Expressing the results as an ordered triple would be (170;120;60)