After a pen is sold at a 35% discount, it is 4.2 yuan cheaper. How much is the original price of this pen?
一支钢笔按六五折出售后，便宜了4.2元，这支钢笔原价多少元？
<gadget id="calculator">65 / 100</gadget>
<output>13/20 = around 0.65</output>

<gadget id="calculator">1 - (13/20)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">4.2 / (7/20)</gadget>
<output>12</output>

<result>12</result>