A ship sails from port A to port B, travels 24 kilometers per hour along the current, and arrives in 15 hours. When returning back against the current, the speed is reduced by 25%. How long will it take to return to Port A? (Solve with ratio)
一艘轮船从甲港开往乙港，去时顺水，每小时行24千米，15小时到达．返回时逆水，速度降低了25%，多少小时返回甲港？(用比例解)
<gadget id="calculator">24 * 15</gadget>
<output>360</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">24 * (1/4)</gadget>
<output>6</output>

<gadget id="calculator">24 - 6</gadget>
<output>18</output>

<gadget id="calculator">360 / 18</gadget>
<output>20</output>

<result>20</result>