Solve 3x+2y-6=0 for y
2y-6=-3x
2y=-3x+6
y=-1.5x+3
So the slope of the reference line is -1.5. For two lines to be parallel they must have the same slope so our line will also have a slope of -1.5 so we have:
y=-1.5x+b, now we can solve for b given the point (0,0)
0=-1.5(0)+b
0=0+b
b=0 so our line is:
y=-1.5x