Incorrect. In order to simplify an expression, first identify like terms, reorder the polynomial, and then combine like terms by adding their coefficients. The terms $\displaystyle{16}{{m}}^{{2}}{n}\usepackage{cmbright}\Huge\$ and $\displaystyle-{5}{n}{{m}}^{{2}}\usepackage{cmbright}\Huge\$ are like terms, while $\displaystyle{6}{m}{{n}}^{{2}}\usepackage{cmbright}\Huge\$ cannot be combined with those two.