Two cars A and B start from east and west at the same time and drive towards each other. Car A travels 48 kilometers per hour, and car B travels 42 kilometers per hour. The two cars meet at a distance of 21 kilometers from the midpoint. Find the two places in the east and west How many kilometers apart.
甲、乙两辆汽车从东西两地同时出发，相向而行，甲车每小时行48千米，乙车每小时行42千米，两车离中点21千米处相遇，求东西两地相距多少千米．
<gadget id="calculator">48 - 42</gadget>
<output>6</output>

<gadget id="calculator">2 / 6</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">48 + 42</gadget>
<output>90</output>

<gadget id="calculator">21 * (1/3) * 90</gadget>
<output>630</output>

<result>630</result>