Xiaobing and Xiaohua hosted the school's blackboard newspaper, and the two could complete it in 3 days of cooperation. After Xiaobing worked for 2 days, Xiaohua continued to work for 1 day. At this time, he completed the blackboard report (2/5). How many days would it take for Xiaohua to run this blackboard newspaper by himself?
小兵和小华主办学校的黑板报，两人合作3天可以完成．小兵做了2天后小华接着做1天，这时共完成了黑板报的(2/5)．如果小华一个人办这期黑板报，需要多少天？
<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(1/3) * 1</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

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

<gadget id="calculator">(1/3) - (1/15)</gadget>
<output>4/15 = around 0.266667</output>

<gadget id="calculator">1 / (4/15)</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>