A copy of "Interesting Mathematics" is 12 yuan after a 20% discount. What is the original price of this book?
一本《趣味数学》打八折后是12元，这本书的原价是多少元．
<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">12 / (4/5)</gadget>
<output>15</output>

<result>15</result>