A number (3/4) is 21 less than 3 times 12, what is this number?
一个数的(3/4)比12的3倍少21，这个数是多少？
<gadget id="calculator">12 * 3</gadget>
<output>36</output>

<gadget id="calculator">36 - 21</gadget>
<output>15</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">15 / (3/4)</gadget>
<output>20</output>

<result>20</result>