The purchase price of a product plus 40 yuan is the selling price. If a customer buys this product with a 20% discount and the store earns 12 yuan, what is the purchase price of this product?
一件商品的进价加上40元是售价，一位顾客买这种商品打八折，商场还赚12元，则这件商品的进价多少元．
<gadget id="calculator">40 - 12</gadget>
<output>28</output>

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

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">28 / (1/5)</gadget>
<output>140</output>

<gadget id="calculator">140 - 40</gadget>
<output>100</output>

<result>100</result>