You may have correctly converted the distance between cities to 280 kilometers, and then solved the proportion $\displaystyle\frac{{80}}{{n}}=\frac{{280}}{{1}}\usepackage{cmbright}\Huge\$ . The correct equation would be $\displaystyle\frac{{{280}\ \text{ kilometers}}}{{n}}=\frac{{{80}\ \text{ kilometers}}}{{{1}\ \text{ hour}}}\usepackage{cmbright}\Huge\$ . The correct answer is $\displaystyle{3}\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ hours.