If the base length is x, the height is 108/x 2 and the surface area is S.
S=x^2+4x* 108/x^2
=x^2+432/x
S'=2x-432/x^2
When S'=0, 2x-432/x 2 = 0.
x ^ 3 = 2 16。
The solution is x=6.
Therefore, when the base length is 6m and the height is108/6 2 = 3m, the material is the least, and at this time, S= 108cm3.