It appears that you multiplied only the first term inside the parentheses by $\displaystyle{\sqrt[{{3}}]{{{y}}}}\usepackage{cmbright}\Huge\$ , and then simplified each term correctly. Make sure to apply the Distributive Property first. Then simplify each term, using $\displaystyle{\sqrt[{{3}}]{{{a}{b}}}}={\sqrt[{{3}}]{{a}}}\cdot{\sqrt[{{3}}]{{b}}}\usepackage{cmbright}\Huge\$ , and combine like terms.