Answer
$x^2+3xy-y^2$
Work Step by Step
Divide $4xy$ to each term of the numerator to have:
$\require{cancel}
\\=\dfrac{4x^3y}{4xy} + \dfrac{12x^2y^2}{4xy}-\dfrac{4xy^3}{4xy}
\\=\dfrac{\cancel{4x^3y}x^2}{\cancel{4xy}} + \dfrac{\cancel{12x^2y^2}3xy}{\cancel{4xy}}-\dfrac{\cancel{4xy^3}y^2}{\cancel{4xy}}
\\=x^2+3xy-y^2$
