While solving the equation $\displaystyle{40}={{h}}^{{2}}-{6}{h}\usepackage{cmbright}\Huge\$ , you may have incorrectly rewritten $\displaystyle-{6}{h}\usepackage{cmbright}\Huge\$ as $\displaystyle{5}{h}-{8}{h}\usepackage{cmbright}\Huge\$ , resulting in a height of 8.