There is a batch of biscuits on the shelf in the supermarket. After they are sold (2/5), the salesperson adds another 8 packs. At this time, the number of packs of biscuits on the shelf is exactly 4 packs less than the original 80%. How many packages of biscuits are there on the shelf?
超市货架上有一批饼干，卖出(2/5)后，营业员又加进了8包，这时货架上饼干的包数恰好比原来的80%少4包．货架上原有饼干多少包？
<gadget id="calculator">8 + 4</gadget>
<output>12</output>

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

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

<gadget id="calculator">1 - (2/5)</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(4/5) - (3/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">12 / (1/5)</gadget>
<output>60</output>

<result>60</result>