A boy travels with a speed of 10 m s^-1 for 30 minute. How much distance does he travel?

Speed = 10 m s^-1
time = 30 minutes
1 min = 60 sec
30 min = 60 x 30 = 1800 sec

distance = ?

$\text{Speed} = \dfrac{\text{distance}}{\text{time}} \\[1em] \text{10} = \dfrac{\text{distance}}{\text{1800}} \\[1em] \text{distance} = 1800 \times 10 = 18000 \text{ m}$

So, distance travelled = 18000 m or 18 km.