\[\boxed{\mathbf{6.76}}\]
\[V = a^{3};\ \ \ S_{поверх} = 6 \cdot a^{2}.\]
\[\textbf{а)}\ a = 3\ м:\]
\[V = 3^{3} = 27\ м^{3}.\]
\[S = 6 \cdot 3^{2} = 6 \cdot 9 = 54\ м^{2}.\]
\[\textbf{б)}\ a = 0,3\ м:\]
\[V = {0,3}^{3} = 0,027\ м^{3}.\]
\[S = 6 \cdot {0,3}^{2} = 6 \cdot 0,09 = 0,54\ м^{2}.\]
\[\textbf{в)}\ a = 0,03\ м:\]
\[V = {0,03}^{3} = 0,000027\ м^{3}.\]
\[S = 6 \cdot {0,03}^{2} = 6 \cdot 0,0009 =\]
\[= 0,0054\ м^{2}.\]