You may have solved the proportion $\displaystyle\frac{{n}}{{100}}=\frac{{18}}{{120}}\usepackage{cmbright}\Huge\$ , but the percent in this problem is 18%. So the correct proportion is $\displaystyle\frac{{18}}{{100}}=\frac{{n}}{{120}}\usepackage{cmbright}\Huge\$ . The answer is 21.6.