First, substitute color(red)(-5) and color(blue)(-1) for color(red)(x) and color(blue)(y) in the first equation and see if both sides of the equation calculate to the same value:
3color(blue)(y) = -2color(red)(x) - 13 becomes:
3 xx color(blue)(-1) = (-2 xx color(red)(-5)) - 13
-3 = 10 - 13
-3 = -3
The first, equation has (-5, -1) as a solution. Now, substitute color(red)(-5) and color(blue)(-1) for color(red)(x) and color(blue)(y) in the second equation and see if both sides of the equation calculate to the same value:
-4color(red)(x) = -8color(blue)(y) + 12 becomes:
-4 xx color(red)(-5) = (-8 xx color(blue)(-1)) + 12
20 = 8 + 12
20 = 20
