A ship travels between A and B. It travels 36 kilometers per hour downstream and 24 kilometers per hour against the current when it returns. It takes 15 hours to go back and forth. How many kilometers is the distance between A and B?
一艘轮船往返于A，B两地，去时顺流每小时行36千米，返回时逆流每小时行24千米，往返一次共用15小时，A，B两地相距多少千米？
<gadget id="calculator">1 / 36</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/36) + (1/24)</gadget>
<output>5/72 = around 0.069444</output>

<gadget id="calculator">15 / (5/72)</gadget>
<output>216</output>

<result>216</result>