On a map with a scale of 1:4,000,000, the distance between A and B is 4.5 cm. Two cars start from A and B at the same time and meet each other after 2 hours. It is known that the express train travels 50 kilometers per hour, and the slow train How many kilometers per hour?
在一幅比例尺是1：4000000的地图上，甲、乙两城相距4.5厘米，两辆汽车同时从甲、乙两地相向出发，2小时后相遇，已知快车每小时行50千米，慢车每小时行多少千米？
<gadget id="calculator">1 / 4_000_000</gadget>
<output>1/4_000_000 = around 0</output>

<gadget id="calculator">4.5 / (1/4_000_000) / 100_000 / 2</gadget>
<output>90</output>

<gadget id="calculator">90 - 50</gadget>
<output>40</output>

<result>40</result>