This may not be your intended question but it is the question that you asked :)
I you meant something different then you need to insert brackets.
$$\frac{3x^2y^5}{6x^3} \times y^4\\\\
=\frac{3x^2y^9}{6x^3}\\\\
=\frac{3xxy^9}{6xxx}\\\\
=\frac{3y^9}{6x}\\\\$$