You may have correctly substituted 5 for $\displaystyle{x}\usepackage{cmbright}\Huge\$ and gotten $\displaystyle{4}{\left({10}-{1}\right)}\usepackage{cmbright}\Huge\$ , but then interpreted this incorrectly as $\displaystyle{4}{\left({10}\right)}-{1}\usepackage{cmbright}\Huge\$ . Using the distributive property, it is correctly rewritten as $\displaystyle{4}{\left({10}\right)}-{4}{\left({1}\right)}\usepackage{cmbright}\Huge\$ .