On a map with a scale of 1:5000000, the distance between A and B is 4 cm. Two cars, A and B, drive from A and B opposite each other. After 4 hours, the two cars meet. Car A travels 30,000 per hour. meters, how many kilometers does a car travel per hour?
在比例尺1：5000000的地图上量得A、B两地的距离为4厘米，甲乙两辆汽车从A，B两地相对开出，4小时后两车相遇，甲辆汽车每小时行30千米，乙辆汽车每小时行多少千米？
<gadget id="calculator">1 / 5_000_000</gadget>
<output>1/5_000_000 = around 0</output>

<gadget id="calculator">4 / (1/5_000_000) / 100_000 / 4</gadget>
<output>50</output>

<gadget id="calculator">50 - 30</gadget>
<output>20</output>

<result>20</result>