Port A and Port B are 480 kilometers apart. A cargo ship departs from Port A to Port B at 9 am, and a passenger ship departs from Port B to Port A at 1 pm. The passenger ship encountered the cargo ship 12 hours after departure. A cargo ship travels 15 kilometers per hour, how many kilometers per hour does a passenger ship travel?
甲、乙两港相距480千米，上午9时一艘货船从甲港出发开往乙港，下午1时一艘客船从乙港出发开往甲港．客船出发12小时后与货船相遇．货船每小时行驶15千米，客船每小时行驶多少千米？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">480 - 60</gadget>
<output>420</output>

<gadget id="calculator">420 / 12</gadget>
<output>35</output>

<gadget id="calculator">35 - 15</gadget>
<output>20</output>

<result>20</result>