$\begin{array}{l}{\text{Here, 8}}^{\text{7}}\times {\left(2^3\right)}^2÷{\text{8}}^{\text{24}}{\text{= 8}}^{\text{?}}\\ \\ \text{Applying the rule of indices, we get}\\ \\ {\text{8}}^{\text{7}}\times {\text{8}}^{\text{2}}÷8^{\text{2.4}}{\text{ = 8}}^{\text{?}}\\ \\ \Rightarrow {\text{ 8}}^{\text{7+2}-\text{2.4}}{\text{=8}}^{\text{?}}\\ \\ \Rightarrow {\text{ 8}}^{\text{?}}{\text{ = 8}}^{\text{9-2.4}}{\text{ = 8}}^{\text{6.6}}\\ \\ \Rightarrow \text{ ? = 6.6}\end{array}$

Hence, Option D is correct.