You have the following expression:
[tex]-6\sqrt[3]{256x^7y^8}[/tex]by simplifying the previous expression you obtain:
[tex]\begin{gathered} -6\sqrt[3]{256x^7y^{8}}=-6\cdot\sqrt[3]{4\cdot64x\cdot x^{6}y^{6}y^{2}}=-6\cdot4x^2y^2\sqrt[3]{4xy^{2}} \\ =-24x^2y^2\sqrt[3]{4xy^2} \end{gathered}[/tex]where you have taken into account to factorize the variables inside the root in a way you can simplify it.
