A piece of iron wire was originally intended to form a rectangular parallelepiped frame with a length of 9 cm and a width and height of 6 cm. Now change it into a cube, what is the side length of the cube?
一根铁丝，原打算围成一个长方体框架，长是9厘米，宽与高都是6厘米．现在改围成一个正方体，围成的正方体棱长是多少厘米？
<gadget id="calculator">9 + 6 + 6</gadget>
<output>21</output>

<gadget id="calculator">4 / 12</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">21 * (1/3)</gadget>
<output>7</output>

<result>7</result>