If the second equation is y=-3x+4 then they would be parallel and I found that by turning the first equation into y=mx+b and you subtract x from both sides of the equation and get -3y=-x+15 and then you divide both sides of the equation by -3 to get the y by itself and that turns into y=1/3x-5 and since 1/3 is the reciprocal of -3 they are perpendicular.
