After the price of a book is reduced (1/4), the current price is 15 yuan. How much is the original price of this book?
一本书降价(1/4)后，现价是15元，这本书原价多少钱？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 / (3/4)</gadget>
<output>20</output>

<result>20</result>