The distance between the cities is $\displaystyle\frac{{{280},{000}\ \text{ meters}}}{{1}}\cdot\frac{{{1}\ \text{ kilometer}}}{{{1},{000}\ \text{ meters}}}\usepackage{cmbright}\Huge\$ , or 280 kilometers.

$\displaystyle\frac{{{280}\ \text{ kilometers}}}{{n}}=\frac{{{80}\ \text{ kilometers}}}{{{1}\ \text{ hour}}}\usepackage{cmbright}\Huge\$

$\displaystyle{n}=\frac{{280}}{{80}}={3}\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$