Find the solution of this system of equations x-8y=21 and 3x--8y=15

If you would like to find the solution of the system of equations, you can do this using the following steps: 

x - 8y = 21    /*(-3)
3x - 8y = 15

-3x + 24y = -63
3x - 8y = 15

-3x + 24y + 3x - 8y = -63 + 15
16y = -48    /16
y = -48/16
y = -3

x - 8y = 21
x = 21 + 8y
x = 21 + 8 * (-3)
x = 21 - 24
x = -3

(x, y) = (-3, -3)

The correct result would be (-3, -3).