On a map with a scale of 1:4000000, the distance between A and B is 20cm. Two trains depart from A and B at the same time. The speed of A train is 87km per hour, and the speed of B train is The hour is 113 km, find the time when the two cars meet.
在比例尺是1：4000000的地图上，量得A，B两地距离是20cm，两列火车同时从A，B两地相对开出，甲车的速度是每小时87km，乙车的速度是每小时113km，求两车相遇的时间．
<gadget id="calculator">1 / 4_000_000</gadget>
<output>1/4_000_000 = around 0</output>

<gadget id="calculator">87 + 113</gadget>
<output>200</output>

<gadget id="calculator">20 / (1/4_000_000) / 100_000 / 200</gadget>
<output>4</output>

<result>4</result>