The selling price of a fountain pen after 25% off is 15 yuan. What is the original price of this fountain pen?
一支钢笔打七五折后的售价是15元，这支钢笔的原价是多少元．
<gadget id="calculator">75 / 100</gadget>
<output>3/4 = around 0.75</output>

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

<result>20</result>