30% of a number is 21, what is 70% of this number?
一个数的30%是21，这个数的70%是多少．
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">21 / (3/10)</gadget>
<output>70</output>

<gadget id="calculator">70 / 100</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">70 * (7/10)</gadget>
<output>49</output>

<result>49</result>