All books in the bookstore are sold with a 20% discount, and a 25% discount if you have a membership card. Buying this book with a membership card saves 8.5 yuan compared to not using a membership card. What is the original price of this book?
书店所有书8折销售，有会员卡再打7.5折，用会员卡买这本书比不用会员卡节约8.5元，这本书原价是多少元．
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">8.5 / (1/4) / (4/5)</gadget>
<output>42.5</output>

<result>42.5</result>