Let’s call the number of student tickets they sold s, and the number of adult tickets they sold a.

The school sold 50 tickets in all, so a+s=50.

For every adult ticket they sold, they made $3, and for every student ticket, they made $2. So the total amount of money they made is 3a+2s. The problem tells us they made $135, so 3a+2s=135.

a + s = 50

3a + 2s = 135

This is a system of equations. We will proceed by changing the first equation, solving for a(we could solve for s instead, but I decided to solve for a). What this means is we will subtract s from both sides to get a alone.

a + s = 50

a = 50 - s

Now we know what a is(in terms of s, that is), so we can plug it into the second equation.

3a + 2s = 135

3(50 - s) + 2s = 135 (Remember to put the parentheses in)

150 - 3s + 2s = 135

150 - s = 135

-s = -15

s = 15

This means 15 student tickets were sold. Plug this into one of the original equations to figure out how many adult tickets were sold:

a + s = 50

a + 15 = 50

a = 35

15 student tickets were sold, and 35 adult tickets were sold.