Adult tickets to the fall play cost $6 and student tickets cost $3. The drama class sold 25 more student tickets than adult tickets to the fall play. If the class collected $660 from ticket sales, how many student tickets were sold?

Let the number of adult tickets sold equal a.
Let the number of student tickets sold equal s.

The cost of the adult tickets sold is 6a.
The cost of the student tickets sold is 3s.
The total sales was $660, so we have our first equation:
6a + 3s = 660

25 more student tickets than adult tickets were sold.
That gives us our second equation
s = a + 25

We have a system of equations.

6a + 3s = 660
s = a + 25

Since the second equation is already solved for s, we can use the substitution method. Replace s of the first equation with a + 25 and solve for a.

6a + 3(a + 25) = 660

6a + 3a + 75 = 660

9a = 585

a = 65

65 adult tickets were sold.
Now we find the number of student tickets sold.

s = a + 25 = 65 + 25 = 90

Answer: The number of student tickets sold was 90.