It takes 10 hours for a passenger ship to sail 900 kilometers down the river with a water speed of 5 kilometers per hour. How long does it take to return?
一艘客轮顺水航行900千米用10小时，水速5千米/小时，它返回需要多少时间？
<gadget id="calculator">900 / 10</gadget>
<output>90</output>

<gadget id="calculator">5 * 2</gadget>
<output>10</output>

<gadget id="calculator">90 - 10</gadget>
<output>80</output>

<gadget id="calculator">900 / 80</gadget>
<output>45/4 = around 11.25</output>

<result>45/4 = around 11.25</result>