If the diagonal of a cube is $8\sqrt{3}\text{ cm}$, then its total surface area is:

Let the side length of the cube be $a$.The formula for the diagonal of a cube is $a\sqrt{3}$.Given:
$$a\sqrt{3}=8\sqrt{3}⟹a=8\text{ cm}$$
The total surface area of a cube is given by $6a^2$:
$$\text{Surface Area}=6\times (8{)}^2=6\times 64=384{\text{ cm}}^2$$