You may have solved the proportion $\displaystyle\frac{{27}}{{100}}=\frac{{180}}{{n}}\usepackage{cmbright}\Huge\$ , but the percent is the amount out of 100 and the amount is 18. So the correct proportion is $\displaystyle\frac{{180}}{{100}}=\frac{{27}}{{n}}\usepackage{cmbright}\Huge\$ .