A boy spends 30 minutes cycling a distance of $8.0\,\text{km}$. He then goes on to walk another distance of $2.0\,\text{km}$ in 15 minutes. What is his average speed?
- A$4.5\,\text{km h}^{-1}$
- B$5.6\,\text{km h}^{-1}$
- C$12\,\text{km h}^{-1}$
- D$13\,\text{km h}^{-1}$