If A and B work together to complete a job in 15 days, and B alone can complete 20% of the job in 4 days, how many days can A alone complete the job?
一件工作，甲、乙合做15天完成，乙独做4天可以完成这件工作的20%，甲独做多少天可以完成这件工作？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) / 4</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/15) - (1/20)</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / (1/60)</gadget>
<output>60</output>

<result>60</result>