For a project, it takes 13 days for A, B, and C to work together. If C rests for 2 days, B will work for 4 more days, or A and B will work together for 1 day. Q: How many days will it take for this project to be done by A alone?
一件工程，甲乙丙三人合作需要13天，如果丙休息2天，乙就要多做4天，或者由甲乙两人合作多做1天．问：这项工程由甲独做需要多少天？
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">3 + 1 + 2</gadget>
<output>6</output>

<gadget id="calculator">3 / 6</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">13 / (1/2)</gadget>
<output>26</output>

<result>26</result>