As shown in the figure, two identical right triangles are stacked together to find the area of the shadow part. (unit: cm)

As shown in the figure, two identical right triangles are stacked together to find the area of the shadow part. (unit: cm)

Because the area of Figure 1 + the area of Figure 2 - the area of Figure 2 + the area of Figure 3, so: the area of Figure 3 = the area of Figure 1, figure 1 is a trapezoid, the upper bottom is 12 cm, the lower bottom is 12-3 = 9 (CM), the height of the trapezoid is 6 cm, so the shadow area of Figure 1 is: (12 + 9) × 6 △ 2 = 21 × 6 △ 2 = 126 △ 2 = 63 (square cm). A: the area of the shadow part is 63 square cm