It takes 13 days for A, B, and C to complete a project. If C rests for 2 days, B will have to do 4 more days, or if A and B work together for 1 day, then the project will be completed by A. Do it alone, how many days will it take.
一项工程，甲、乙、丙三人合作需13天完成，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，那么这项工程由甲独做，需要多少天．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

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