Using the FOIL method, you find:

$\displaystyle{\left({8}{n}-{3}\right)}{\left({5}{n}+{7}\right)}={8}{n}{\left({5}{n}\right)}+{8}{n}{\left({7}\right)}-{3}{\left({5}{n}\right)}-{3}{\left({7}\right)}={40}{{n}}^{{2}}+{56}{n}-{15}{n}-{21}={40}{{n}}^{{2}}+{41}{n}-{21}\usepackage{cmbright}\Huge\$