A project can be completed in 5 days if 4 A-type excavators are used; if 4 A-type excavators and 2 B-type excavators are used, it can be completed in 3 days; if 3 B-type excavators are used machine and 9 C-type excavators, can be completed in 2 days. Now, one type A, one type B and one type C excavator have been working together for 6 days, and only one type A excavator is left to continue working. How many more days will it take to complete this project?
一项工程，如果用4台A型挖土机，5天可以完成；如果用4台A型挖土机和2台B型挖土机，3天可以完成；如果用3台B型挖土机和9台C型挖土机，2天可以完成．现在A型、B型和C型挖土机各一台一起工作6天后，只余下一台A型挖土机继续工作，问再用多少天就可以完成这项工程？
<gadget id="calculator">1 / 4 / 5</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 4 * 3</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) / 3 / 2</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/15) * 2 * 3</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(3/5) / 9 / 2</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/15) + (1/30)</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/20) * 6</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">1 - (9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) / (1/20)</gadget>
<output>2</output>

<result>2</result>