Correct. There are only two $\displaystyle{{a}}^{{2}}{{b}}^{{3}}\usepackage{cmbright}\Huge\$ terms in these polynomials: $\displaystyle-{4}{{a}}^{{2}}{{b}}^{{3}}+{12}{{a}}^{{2}}{{b}}^{{3}}={\left(-{4}+{12}\right)}{{a}}^{{2}}{{b}}^{{3}}={8}{{a}}^{{2}}{{b}}^{{3}}\usepackage{cmbright}\Huge\$

So 8 is the coefficient.