Port A and Port B are 360 kilometers apart. A steamship sails from Port A to Port B and arrives in 15 hours along the current. From Port B back to Port A, it sails upstream in 20 hours. Now there is a motor sailboat with a speed of 12 kilometers per hour. How many hours does it take to go back and forth between the two ports?
甲、乙两港相距360千米，一艘轮船从甲港到乙港，顺水航行15小时到达，从乙港返回甲港，逆水航行20小时到达．现在有一艘机帆船，船速是每小时12千米，它往返两港需要多少小时？
<gadget id="calculator">360 / 15</gadget>
<output>24</output>

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

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

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">12 + 3</gadget>
<output>15</output>

<gadget id="calculator">12 - 3</gadget>
<output>9</output>

<gadget id="calculator">360 / 9</gadget>
<output>40</output>

<gadget id="calculator">24 + 40</gadget>
<output>64</output>

<result>64</result>