It takes 13 days for A, B, and C to complete the project. If C rests for two days, B will have to work for 4 more days, or A and B will work together for an extra day. How many days will it take for A to do this project alone? ?
甲、乙、丙三人合作需13天完成，如果丙休息两天，乙就要多做4天，或者由甲、乙两人合作多做1天，问这项工程甲独做需多少天？
<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>