Two cars A and B are driving toward each other at the same time from two places 1200 kilometers apart. Car A travels 60 kilometers per hour. When the car reaches the midpoint of the two places, it is 100 kilometers away from car B. Find the speed of car B.
甲乙两车同时从相距1200千米的两地相向而行，甲车每小时行60千米，当驾车行到两地中点时，与乙车相距100千米．求乙车的速度．
<gadget id="calculator">600 - 100</gadget>
<output>500</output>

<gadget id="calculator">600 / 60</gadget>
<output>10</output>

<gadget id="calculator">500 / 10</gadget>
<output>50</output>

<result>50</result>