A book is 15mm thick, and 4 books are stacked together, what is the thickness in centimeters?
一本书厚15毫米，4本书摞在一起，厚多少厘米．
<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">15 * (2/5)</gadget>
<output>6</output>

<result>6</result>