Решение:
\[ \frac{3(6a^5)^2}{a^7} = \frac{3 \times 6^2 \times (a^5)^2}{a^7} = \frac{3 \times 36 \times a^{10}}{a^7} = 108 \times a^{10-7} = 108a^3 \]
\[ 108 \times (\sqrt{8})^3 = 108 \times (8^{1/2})^3 = 108 \times 8^{3/2} \]
\[ 8^{3/2} = (8^{1/2})^3 = (\sqrt{8})^3 = (2\sqrt{2})^3 = 2^3 \times (\sqrt{2})^3 = 8 \times 2\sqrt{2} = 16\sqrt{2} \]
\[ 108 \times 16\sqrt{2} = 1728\sqrt{2} \]
Ответ: 1728√2