#### A boy covers a distance of 30 km in 5 hours partly on foot at the rate of 3.5 kmph and partly on cycle at 9kmph. Find the distance covered on foot.

Let the distance covered on foot be x km.
Then, the distance covered on bicycle= (30-x)km
Time taken to cover x km at 3.5 kmph = $\frac{x}{3.5}hours$
Time taken to cover (30-x) km at 9kmph = $(\frac{30-x}{9})hours$
$\therefore \frac{x}{3.5}+\frac{30-x}{9}=5$

$\Rightarrow \frac{10x}{35}+\frac{30-x}{9}=5$
$\Rightarrow \frac{90x+35(30-x)}{315}=5$

$\Rightarrow 90x+1050-35x=1575$

$\Rightarrow 55x=525$

$\Rightarrow x=9.54$

Hence the distance covered by foot is 9.54 km.