You can
put this solution on YOUR website!by definition,
so

is

and

is
so, for yours...

, we get
and then this becomes -y/3. The negative sign can remain on top...it doesn't matter as the 3 is -ve and the y is +ve, swapping them in the fraction, we still have a + and -... making a -ve.
remember, you can always take a numerical example to test...

should be 3/4, which it is on the calculator.
Does that help?
jon.