They are similar by number. But they are not perpendicular. 3x+4y=12 gives you a negative slope. But 4x-3y gives you a positive slope. So they would be crossing each other if put together. This means that Sadia is correct and Henri isn’t. Show all work: 4x-3y=12
4x-3y+3y=12+3y
4x=3y+12
4x/4=3y+12/4
X=3/4y+3
3x+4y=12
3x+4y+-4y=12+-4y
3x=-4y+12
3x/3=-4y+12/3
X=-4/3y+4