Consider the rectangular prism shown with its height is 12m and the length of its base is $(x+4)m$ and $(x+8)m$ respectively.

Write a fully expanded and simplified expression for the volume of the prism.
Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: Consider the rectangular prism shown with its height is 12m and the length of its base is $(x+4)m$ and $(x+8)m$ respectively.

Write a fully expanded and simplified expression for the volume of the prism.
Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: Consider the rectangular prism shown with its height is 12m and the length of its base is $(x+4)m$ and $(x+8)m$ respectively.

Write a fully expanded and simplified expression for the volume of the prism.