ANSWER
9cm
EXPLANATION
The volume of a square pyramid is calculated using the formula;
[tex]V = \frac{1}{3} {l}^{2}h[/tex]
where h=12cm is the height of the pyramid and l is the length of each side of the square base.
The volume is V=324.
We substitute the values in to the formula and solve for l.
[tex]324 = \frac{1}{3} {l}^{2} \times 12[/tex]
[tex]324 = 1 {l}^{2} [/tex]
[tex] {l}^{2} = \frac{324}{4} [/tex]
[tex] {l}^{2} = 81[/tex]
[tex]l = \sqrt{81} = 9[/tex]
The length of each side of the square base is 9 cm.