Two warships A and B are constantly patrolling between the two military bases. The speed of ship A is 12 kilometers per hour, and the speed of ship B is 9 kilometers per hour. The two ships set off from the two bases at the same time, and it happened that it took 6 hours for the first encounter. How many kilometers are there between these two military bases?
甲乙两艘军舰不停地往返于两个军事基地之间巡逻．甲舰时速12千米，乙舰时速9千米，两舰从两个基地同时相向出发，第一次相遇时恰巧用了6小时．这两个军事基地之间有多少千米？
<gadget id="calculator">12 + 9</gadget>
<output>21</output>

<gadget id="calculator">21 * 6</gadget>
<output>126</output>

<result>126</result>