For a project, A works alone for 2 days first, and then cooperates with B for 7 days, so that half of the whole project can be completed. It is known that the work-efficiency ratio of A and B is 2:3. If the work is done by B alone, how many days will it take to complete it?
一项工程，甲先单独做2天，然后与乙合做7天，这样才能完成全工程的一半．已知甲、乙的工效比是2：3．如果这项工程由乙单独做，需要多少天才能完成？
<gadget id="calculator">2 + 7</gadget>
<output>9</output>

<gadget id="calculator">2 / 3</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">9 * (2/3) * 2</gadget>
<output>12</output>

<gadget id="calculator">7 * 2</gadget>
<output>14</output>

<gadget id="calculator">12 + 14</gadget>
<output>26</output>

<result>26</result>