It appears that you combined the terms in the order in which they were written, combining unlike terms such as 12 with $\displaystyle{{x}}^{{2}}\usepackage{cmbright}\Huge\$ to obtain $\displaystyle{12}{{x}}^{{2}}\usepackage{cmbright}\Huge\$ . Be sure to combine only like terms. The correct answer is $\displaystyle-{{x}}^{{3}}+{{x}}^{{2}}-{9}{x}+{17}\usepackage{cmbright}\Huge\$ .