Two fast and slow trains leave opposite cities at the same time. The express train travels 90 kilometers per hour, and the slow train travels 70 kilometers per hour. After 9 hours, the two trains meet at a certain railway station. How many kilometers are there between the two cities?
快慢两列火车同时从甲乙两城相对开出，快车每小时行90千米，慢车每小时行70千米，9小时后，两车在某火车站相遇．甲乙两城相距多少千米？
<gadget id="calculator">90 + 70</gadget>
<output>160</output>

<gadget id="calculator">160 * 9</gadget>
<output>1_440</output>

<result>1_440</result>