Wang Jun bought a book and a pen. The price of the book is 4 yuan, which belongs to the pen (2/5). How much is the price of the pen?
王军买了一本书和一支笔，书的价格4元，是笔的(2/5)，笔的价格是多少元？
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">4 / (2/5)</gadget>
<output>10</output>

<result>10</result>