You may not have noticed the index of the cube root, and so incorrectly combined all the radicals, while not simplifying the square roots. Start by simplifying the first and last terms using $\displaystyle\sqrt{{{a}{b}}}=\sqrt{{a}}\cdot\sqrt{{b}}\usepackage{cmbright}\Huge\$ . Now the first and last terms are like terms that you can combine, just as you would combine $\displaystyle{16}{a}+{3}{a}\usepackage{cmbright}\Huge\$ .