A project can be completed by 3 people from Group A in 8 days and 4 people from Group B in 7 days. Now, 2 people from Group A and 7 people from Group B can complete it in how many days? (special engineering questions)
一项工程，甲组3人8天能够完成，乙组4人7天能够完成，现在由甲组2人和乙组7人合作，多少天可以完成？(特殊工程问题)
<gadget id="calculator">3 * 8</gadget>
<output>24</output>

<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

<gadget id="calculator">(1/24) * 2</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">4 * 7</gadget>
<output>28</output>

<gadget id="calculator">1 / 28</gadget>
<output>1/28 = around 0.035714</output>

<gadget id="calculator">(1/28) * 7</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/12) + (1/4)</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 / (1/3)</gadget>
<output>3</output>

<result>3</result>