Adding this number to 3 times of a number gives 81.6. Find this number.
一个数的3倍加上这个数得81.6，求这个数．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<gadget id="calculator">81.6 / 4</gadget>
<output>20.4</output>

<result>20.4</result>