解答上面的题目，使用一些flash动图来帮助解释---**Extraction Content:** **Textual Information:** * **Question Number:** 7、 * **Question Stem:** 一张斜边长 30cm 的绿色直角三角形纸片、一张斜边长 20cm 的红色直角三角形纸片和一张白色正方形纸片拼成一个直角三角形, 红色直角三角形纸片和绿色直角三角形纸片的面积之和是多少? (Translation: A piece of green right-angled triangle paper with hypotenuse length 30cm, a piece of red right-angled triangle paper with hypotenuse length 20cm, and a piece of white square paper are assembled into a right-angled triangle. What is the sum of the areas of the red right-angled triangle paper and the green right-angled triangle paper?) * **Options:** None * **Other Relevant Text:** Units are in cm (centimeters). **Chart/Diagram Description:** * **Type:** Geometric diagram illustrating the assembly of three shapes (two right-angled triangles and a square) into a larger right-angled triangle. * **Main Elements:** * A large right-angled triangle is formed by the assembly. The right angle of this large triangle is located at the bottom right vertex of the diagram. Its legs are along the bottom horizontal edge and the right vertical edge. Its hypotenuse is the slanted line on the top left. * A white shape, labeled "白色" (white), is a square placed in the bottom right corner of the large triangle. One vertex of the square is at the right angle vertex of the large triangle. Two sides of the square lie along the legs of the large triangle. Right angle marks are shown at two vertices of the square (including the vertex at the right angle of the large triangle). * A green shape, labeled "绿色" (green), is a right-angled triangle located to the left of the white square, along the bottom leg of the large triangle. Its right angle is marked at the vertex where it meets the bottom leg of the large triangle and the left side of the white square. One leg of the green triangle is along the bottom leg of the large triangle. The other leg is the left side of the white square. The hypotenuse of the green triangle is the slanted side (length 30cm, as per the text). * A red shape, labeled "红色" (red), is a right-angled triangle located above the white square, along the right leg of the large triangle. Its right angle is marked at the vertex where it meets the right leg of the large triangle and the top side of the white square. One leg of the red triangle is along the right leg of the large triangle. The other leg is the top side of the white square. The hypotenuse of the red triangle is the slanted side (length 20cm, as per the text). * The diagram shows the three shapes perfectly fitting together to form the large right-angled triangle.