The factors have not been regrouped. After substitution you will have $\displaystyle{\left({4}\cdot{\left(-\frac{{1}}{{6}}\right)}\right)}\cdot{3}\usepackage{cmbright}\Huge\$ . If you use the commutative property and then multiply and simplify, you will get this answer. The correct answer is: $\displaystyle{4}\cdot{\left(-\frac{{1}}{{2}}\right)}\usepackage{cmbright}\Huge\$