\(=3\left(x-y\right)+\left(x-y\right)\left(x+y\right)\)
\(=\left(x-y\right)\left(x+y+3\right)\)
\(=3\left(x-y\right)+\left(x-y\right)\left(x+y\right)=\left(x-y\right)\left(x+y+3\right)\)
3x - 3y + x2 - y2
= (3x - 3y) + (x2 - y2)
= 3(x - y) + (x - y)(x + y)
=(3 + x + y)(x - y)