The propagation speed of sound in the air is 340 m/s. Zhang Xiao shouted to the distant mountain, and heard the echo after 4 seconds. How many meters is Zhang Xiao from the mountain?
声音在空气中的传播速度是340米/秒，张晓对着远处的大山喊话，经过4秒听见了回音，张晓离大山有多少米．
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">340 * 2</gadget>
<output>680</output>

<result>680</result>