1. The problem asks to find the total number of small unit cubes in the 3D block structure described. 2. Let's analyze the description step-by-step: - Bottom row: 3 cubes in a line. - On top of the first bottom cube on the left, there is 1 cube stacked, so that column has 2 cubes. - To the right of the stacked cube, there is a flat L-shaped section made of 4 cubes arranged in a 2x2 grid with one additional cube on top at the right corner. This means 4 cubes on the base plus 1 cube on top, totaling 5 cubes in this section. - At the center of the figure, there is a vertical stack of 4 cubes rising above the base. 3. Now, let's count all cubes: - Bottom row: 3 cubes - Stacked cube on the first bottom cube: 1 cube - L-shaped section: 5 cubes - Vertical stack at center: 4 cubes 4. Add all these cubes: $$3 + 1 + 5 + 4 = 13$$ 5. Therefore, the total number of cubes in the structure is 13.