The side length of a square is acm, if the side length is reduced by 6cm, the area is reduced by 72cm**2, then a=how much.
一个正方形边长为acm，若边长减少6cm，面积减少72cm**2，则a=多少．
<gadget id="calculator">72 + 36</gadget>
<output>108</output>

<gadget id="calculator">108 / 12</gadget>
<output>9</output>

<result>9</result>