An amusement park sells adult tickets and children tickets, with adult tickets costing $5 and children's tickets costing $3 if Ed bought 15 tickets and spent a total of $57, how many children's tickets did he buy?

He buy 6 children tickets

Step-by-step explanation:

First we have to perform 2 equations, one indicating the number of tickets and the other the total amount

x = Adult tickets

y = Children tickets

x + y = 15

x * $5 + y * $3 = $57

we clear the x from the first equations

x + y = 15

x = 15 - y

we replace the value of x in the second equation with (15 - y) and solve

x * $5 + y * $3 = $57

(15 - y) * 5 + y * 3 = 57

75 - 5y + 3y = 57

-5y + 3y = 57 - 75

-2y = - 18

y = - 18/-2

y = 9

we replace y in the first equation

x = 15 - y

x = 15 - 9

x = 6

He buy 6 children tickets