A 160-kilometer-long waterway takes Ship A 8 hours to travel downstream and 20 hours to travel upstream. If it takes boat B 10 hours to go downstream, how many hours does it take boat B to go upstream?
一条长160千米的水路，甲船顺流而下需要8小时，逆流而上需要20小时．如果乙船顺流而下要10小时，那么乙船逆流而上需要多少小时？
<gadget id="calculator">160 / 8</gadget>
<output>20</output>

<gadget id="calculator">160 / 20</gadget>
<output>8</output>

<gadget id="calculator">20 - 8</gadget>
<output>12</output>

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">10 - 6</gadget>
<output>4</output>

<gadget id="calculator">160 / 4</gadget>
<output>40</output>

<result>40</result>