82 minus 4 times a number, the difference is 30, find this number.
82减去一个数的4倍，差是30，求这个数．
<gadget id="calculator">82 - 30</gadget>
<output>52</output>

<gadget id="calculator">52 / 4</gadget>
<output>13</output>

<result>13</result>