8-3x
If you mean: y = -3x, then the line y = -3x+2 will be parallel to it because they both have the same slope.
If: 3x+y = -4 Then: y = -3x-4 and the slope of the line is -3
If you mean y = -3x -6 then the slope of the line is -3
It has no asymptote. 3x is a straight line and therefore is a tangent to itself.