Solve the equation: x-(x-800)*20%=2640.
解方程：x-(x-800)*20%=2640．
<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>