car is driving towards the valley at a speed of 20 meters per second. The driver presses the horn, and hears the echo from the valley 4 seconds later. How many meters was the car from the valley when the horn was honked? (The speed of sound in air is 340 meters per second)
一辆汽车以每秒20米的速度向山谷方向行驶，司机按了一声喇叭，4秒后听到从山谷中传来的回声．按喇叭时汽车离山谷有多少米？(声音在空气中传播的速度是每秒340米)
<gadget id="calculator">340 * 4</gadget>
<output>1_360</output>

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">1_360 + 80</gadget>
<output>1_440</output>

<gadget id="calculator">1_440 / 2</gadget>
<output>720</output>

<result>720</result>