If a product is sold according to the seasons, if it is sold at a 10% discount on the current price, it will still make a profit of 180 yuan; if it is sold at a 20% discount, it will lose 240 yuan. How much is the purchase price of this item?
一件商品随季节变化出售，如果按现价打九折出售，仍可盈利180元；如果打八折出售，就亏损240元．这件商品进价是多少元？
<gadget id="calculator">240 + 180</gadget>
<output>420</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(9/10) - (4/5)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">420 / (1/10)</gadget>
<output>4_200</output>

<gadget id="calculator">4_200 * (9/10)</gadget>
<output>3_780</output>

<gadget id="calculator">3_780 - 180</gadget>
<output>3_600</output>

<result>3_600</result>