Okay, here we have this:
First we are going to convert the equation to the form slope-intersect:
6x+3y=-18 -6x+3y=-18
3y=-18-6x 3y=-18+6x
y=(-18-6x)/3 y=(-18+6x)/3
y=-2x-6 y=2x-6
Now, if we graph the equations we obtain the following:
The solution to the equation system are the points where the lines intersect, therefore the only solution we obtain is (0, -6)