To solve the problem of finding the number of cubes with exactly two faces painted, we follow these steps:

Key Insight:

For a rectangular prism (block) with dimensions (l \times w \times h) (in meters, cut into 1m³ cubes), cubes with exactly two faces painted lie along the edges excluding the corners (corners have 3 faces painted).

Each edge of length (k) (number of cubes along that edge) contributes ((k-2)) cubes with two faces painted (since we remove the 2 corner cubes). There are 4 edges for each dimension (total 12 edges).

Calculation Example (Assuming common problem dimensions: 2m×3m×4m):

• For 2m edge: ((2-2) = 0) cubes per edge, 4 edges → (0×4=0)
• For 3m edge: ((3-2)=1) cube per edge, 4 edges → (1×4=4)
• For 4m edge: ((4-2)=2) cubes per edge,4 edges → (2×4=8)

Total two-faced painted cubes: (0+4+8=12)

Answer: (\boxed{12})

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