Cars A and B drive from city A to city B at speeds of 100 kilometers and 120 kilometers per hour respectively. Car A leaves city A 1 hour earlier than car B, but arrives at city B at the same time. Find the distance between the two cities ．
汽车甲和乙分别以每小时100千米和120千米的速度从A城开往B城，甲车比乙车早1小时离开A城，但同时到达B城，求两城之间的路程．
<gadget id="calculator">120 - 100</gadget>
<output>20</output>

<gadget id="calculator">100 / 20</gadget>
<output>5</output>

<gadget id="calculator">5 * 120</gadget>
<output>600</output>

<result>600</result>