1. Find a piece of paper big enough to draw an expanded diagram of the cuboid on the paper. As shown in the figure below:

When drawing, make sure that the red line is 3cm, the yellow line is 5cm and the green line is 7cm.

1, 2, 3, 4, 5 and 6 are all rectangles in the expansion diagram. Among them, Figure 1 and Figure 2 are 7 cm long and 5 cm wide.

The length of Figures 2 and 4 is 7 cm and the width is 3 cm. Figs. 5 and 6 are 5 cm in length and 3 cm in width.

2. Cut the unfolded figure along the chalk line (as shown in the figure below):

3. Fold the paper along the black line. When folding paper, make sure that 1 faces 2, 3 and 4, and 5 and 6.

4. After folding, paste it with transparent glue.

Knowledge about cuboids:

1. The cuboid is a three-dimensional figure with six faces, and every two opposite faces have the same size.

As shown below: the red and blue sides are the same size.

In the picture above, all six faces of the cuboid are rectangles.

The six faces of a cuboid may also have squares (when side a= side B in the figure, both faces are squares), as shown in the figure.

2. A cuboid has 12 sides, and four opposite sides are equal in length.

The three sides drawn from the same vertex are called length, width and height respectively. As shown below, the three green edges drawn from the red vertex are the length, width and height of the cuboid.

3. The formula of cuboid area =(a*b+a*c+b*c)X2.

4. cuboid volume formula = length × width × height