# A car is moving with a speed of 72 kmph towards a hill. Car blows horn at a distance of 1800 m from the hill. If echo is heard after 10 seconds, the speed of sound (in m/sec.) is

$\begin {array} {1 1} (1)\;300 & \quad (2)\;320 \\ (3)\;340 & \quad (4)\;360 \end {array}$

(3) 340