One way to look at it would be to solve for y - if what x is multiplied by is the same for both sides, they're parallel. If one is the negative reciprocal (e.g. for 5/6 the reciprocal is 6/5 and the negative reciprocal is therefore -6/5) of another, they're perpendicular and if they're neither they're neither.Solving for y in x+5y=4, we can subtract x from both sides to get 5y=-x+4. Next, we can divide both sides by 5 to get -x/5+4=y. Since -x/5=(-1/5)(x) and -1/5 is not the negative reciprocal of 5/6 as established earlier, they are neither