A farmer covered a total distance of $70\text{km}$ in $10\text{hours}$. He travelled part of the distance on foot at a speed of $5\text{km/h}$ and the remaining distance by bicycle at a speed of $10\text{km/h}$. Find the distance travelled on foot.

1. A
   $25\text{km}$
2. B
   $45\text{km}$
3. C
   $30\text{km}$
4. D
   $50\text{km}$