Ship A sailed along the current for 3 hours, traveled 180 kilometers, and returned to the original place in 6 hours; Ship B sailed along the same waterway in 4 hours. How many hours did it take for ship B to return to the original place?
甲船顺水航行用了3小时，行了180千米，返回原地用了6小时；乙船顺水航行同一段水路用了4小时，乙船返回原地比去时需多用几小时？
<gadget id="calculator">180 / 4</gadget>
<output>45</output>

<gadget id="calculator">180 / 3</gadget>
<output>60</output>

<gadget id="calculator">180 / 6</gadget>
<output>30</output>

<gadget id="calculator">60 - 30</gadget>
<output>30</output>

<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">45 - 15 - 15</gadget>
<output>15</output>

<gadget id="calculator">180 / 15</gadget>
<output>12</output>

<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<result>8</result>