If the side length of a square increases by 4cm, then its area increases by 64cm**2. Find the side length of the square.
如果一个正方形的边长增加4cm，那么它的面积就增加64cm**2，求这个正方形的边长．
<gadget id="calculator">64 - 16</gadget>
<output>48</output>

<gadget id="calculator">48 / 8</gadget>
<output>6</output>

<result>6</result>