Teacher Shi received a manuscript fee for the books of the publishing house. After deducting the manuscript fee of 800 yuan, he needs to pay personal income tax at a rate of 20%. After paying the tax, he gets 2640 yuan. How much is the manuscript fee?
施老师因出版社图书获得一笔稿费，稿费扣除800元后需要按照20%的税率缴纳个人所得税，缴税后获得2640元．这笔稿费有多少元？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">800 * (1/5)</gadget>
<output>160</output>

<gadget id="calculator">2_640 - 160</gadget>
<output>2_480</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">2_480 / (4/5)</gadget>
<output>3_100</output>

<result>3_100</result>