A lamp, each priced at 15 yuan after a 20% discount, how much is the price reduction, and what is the correct list
一台灯，打八折后每个售价15元，降价多少元，正确列式为多少
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">15 / (4/5)</gadget>
<output>75/4 = around 18.75</output>

<gadget id="calculator">(75/4) - 15</gadget>
<output>15/4 = around 3.75</output>

<result>15/4 = around 3.75</result>