car with a speed of 72 kilometers per hour is driving towards a sounding wall in the front direction. It takes 4.5 seconds to hear the echo after the whistle is blown. The known speed of sound in the air is 340 meters per second. Listen How far away is the car from the sound bar when the echo arrives?
一辆速度为每小时72千米的汽车，向正前方向的一个回音壁驶去，鸣笛后4.5秒钟才听到回声，己知声音在空气中的速度是每秒钟340米，听到回声时汽车离回音壁还有多远？
<gadget id="calculator">340 * 4.5</gadget>
<output>1_530</output>

<gadget id="calculator">4.5 * 20</gadget>
<output>90</output>

<gadget id="calculator">1_530 + 90</gadget>
<output>1_620</output>

<gadget id="calculator">1_620 / 2</gadget>
<output>810</output>

<gadget id="calculator">810 - 90</gadget>
<output>720</output>

<result>720</result>