A train travels 936 kilometers from City A to City B in the first 12 hours. According to this speed, it takes 21 hours to reach City B. How many kilometers is the railway between A and B?
一列火车从甲城开往乙城，前12小时行驶了936千米．照这样的速度，到达乙城共用21小时，甲乙两城之间铁路长多少千米？
<gadget id="calculator">936 / 12</gadget>
<output>78</output>

<gadget id="calculator">78 * 21</gadget>
<output>1_638</output>

<result>1_638</result>