Students sold 400 tickets to the spring band concert. the students sold adult and child (under 12 years old) tickets. each adult ticket was $5.00 and each child ticket was $2.00. the total amount of money earned from the sale of tickets was $1475

You will have a system of equations.
Let's say that the number of adult tickets sold is x. The number of child ticket sold is y.
We know that they sold 400 tickets, so: x + y = 400
We also know that they earned $1475
An adult ticket is $5 and a child ticket is $2, so: x * 5 + y * 2 = 1475
Because x + y = 400, we know that y = 400 - x. We use this in the main equation instead of the variable y:
x * 5 + (400-x) * 2 = 1475
5x + 800 - 2x = 1475
3x + 800 = 1475
3x = 675
x = 225

Because x + y = 400, we can calculate that y = 175

They sold 225 adult tickets and 175 child tickets.