For a piece of cloth, if (3/4) of it is used, there will be 15 meters left; if (3/5) of it is used, how many meters will be used.
一段布，用去它的(3/4)，就剩下15米；若用去它的(3/5)，则用去多少米．
<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">1 - (3/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">15 / (1/4)</gadget>
<output>60</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">60 * (3/5)</gadget>
<output>36</output>

<result>36</result>