A project can be completed by the cooperation of A and B in 8 hours. If A can complete the project in 20 hours alone, how many hours will it take for B to complete the whole project (3/10) alone?
一项工程，甲乙二人合作8小时可以完成．甲独做20小时可以完成，乙独做全工程的(3/10)要多少小时．
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/8) - (1/20)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">(3/10) / (3/40)</gadget>
<output>4</output>

<result>4</result>