Multiply each term in the first binomial with each term in the second binomial, and then combine the two like terms. It appears that you multiplied the first two terms and the last two terms, but $\displaystyle{8}{n}{\left({7}\right)}\usepackage{cmbright}\Huge\$ and $\displaystyle-{3}{\left({5}{n}\right)}\usepackage{cmbright}\Huge\$ are missing.