Subtract 45 from 12 times a number, the difference is 39, find this number. (solution by equation)
一个数的12倍减去45，差是39，求这个数．(用方程解)
<gadget id="calculator">39 + 45</gadget>
<output>84</output>

<gadget id="calculator">84 / 12</gadget>
<output>7</output>

<result>7</result>