The moon travels 8 kilometers per second around the earth, and the earth travels 29 kilometers per second around the sun. How many kilometers per second does the earth travel further than the moon.
月亮每秒绕地球行8千米，地球绕太阳每秒行29千米．地球比月亮每秒多行多少千米．
<gadget id="calculator">29 - 8</gadget>
<output>21</output>

<result>21</result>