3/5 of a number is 21, what is this number?
一个数的3/5是21，这个数是多少．
<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">21 / (3/5)</gadget>
<output>35</output>

<result>35</result>