A set of "Encyclopedia", after a 15% discount, is 425 yuan per set, how much is the discount.
一套《大百科全书》，实行八五折优惠后，每套425元，优惠了多少元．
<gadget id="calculator">85 / 100</gadget>
<output>17/20 = around 0.85</output>

<gadget id="calculator">425 / (17/20)</gadget>
<output>500</output>

<gadget id="calculator">500 - 425</gadget>
<output>75</output>

<result>75</result>