The car drove straight towards the silent valley at a speed of 72 kilometers per hour. The driver honked the horn. After 4 seconds, the echo was reflected by the mountains behind the valley. It is known that the speed of sound is 340 meters per second, and the echo was heard. What is the distance between the car and the mountain in meters?
汽车以每小时72千米的速度笔直地开向寂静的山谷，驾驶员按一声喇叭，4秒后经山谷后面的大山反射听到回声，已知声音的速度是每秒340米，听到回声时汽车离大山的距离是多少米．
<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">340 * 4</gadget>
<output>1_360</output>

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

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

<gadget id="calculator">720 - 80</gadget>
<output>640</output>

<result>640</result>