3.5 times a number is 30 less than the product of 20.5 and 3. Find this number.
一个数的3.5倍比20.5与3的积少30，求这个数．
<gadget id="calculator">20.5 * 3</gadget>
<output>61.5</output>

<gadget id="calculator">61.5 - 30</gadget>
<output>31.5</output>

<gadget id="calculator">31.5 / 3.5</gadget>
<output>9</output>

<result>9</result>