$${23\, \mathrm{hippikoni/h} = \left( 23 \frac{\mathrm{hippikoni}}{\mathrm{h}} \right) \left(\frac{4\, \mathrm{staadionit}}{1\, \mathrm{hippikon}} \right) \left( \frac{6\, \mathrm{plethrat}}{1\, \mathrm{staadion}} \right) \\ \times \left( \frac{30,8\, \mathrm{m}}{1\, \mathrm{plethron}} \right) \left( \frac{1\, \mathrm{km}}{1000\, \mathrm{m}} \right) \left( \frac{1\, \mathrm{h}}{3600\, \mathrm{s}} \right) \\ = 4,7227 \times 10^{-3}\, \mathrm{km/s} \approx \underline{\underline{ 4,7 \times 10^{-3}\, \mathrm{km/s}}}}$$