Step 1: Analyze the existing stack.
The existing stack consists of bricks in a 3D arrangement, but it is not a complete rectangular block. The missing bricks are those that would fill the gaps to complete the rectangular block.
Step 2: Count the total number of bricks in the rectangular block.
If the stack were a complete rectangular block, it would have dimensions given by the length, width, and height of the arrangement. Let's assume the dimensions of the block are \(3 \times 3 \times 4 = 36\) bricks.
Step 3: Count the bricks already in the stack.
By counting the visible bricks in the current stack, there are 24 bricks.
Step 4: Calculate the missing bricks.
To complete the stack into a rectangular block, the missing number of bricks is:
\[
\text{Missing bricks} = 36 - 24 = 12.
\]
\[
\boxed{12}
\]