Evaluate: $\dfrac{(x+y)^2 - (x-y)^2}{y}$ for $x=6$, $y \not= 0$.

( x + y)^2  - (x - y)^2

_________________           factor the numerator as a difference of squares

              y 

[ ( x + y) + ( x - y) ] [ (x + y)  - (x - y) ]

_______________________________

                        y

[  2x] [ 2y ]

_________  =

        y

4x =

4(6)  =

24