这道题怎么做？小学4年级，不能用高年级的方法---**Extracted Content:** **Question Stem:** (10) 如图, 大长方形面积 60 平方厘米, 小长方形面积 40 平方厘米, 求阴影三角形面积。 **Translation of Question Stem:** (10) As shown in the figure, the area of the large rectangle is 60 square centimeters, the area of the small rectangle is 40 square centimeters. Find the area of the shaded triangle. **Other Relevant Text:** * "中点" (midpoint) - A label pointing to a point on the left side of the large rectangle. **Chart/Diagram Description:** * **Type:** Geometric figure, composed of a large outer rectangle containing a smaller rectangle in its bottom-left corner, and a shaded triangular region in its top-left corner. Various lines are drawn within these shapes. * **Main Elements:** * **Large Rectangle:** This is the outermost bounding box of the entire figure. It represents the "大长方形" (large rectangle) mentioned in the problem statement. * **Small Rectangle:** A smaller rectangular region is located in the bottom-left corner of the large rectangle. This region is explicitly shown with its two diagonals drawn, forming an 'X' shape within it. This represents the "小长方形" (small rectangle) mentioned in the problem statement. The small rectangle shares its bottom-left vertex and its left and bottom sides with the large rectangle. * **Midpoint:** A point is marked on the left vertical side of the large rectangle, labeled "中点" (midpoint). This indicates it is the midpoint of that side. * **Shaded Region:** A triangular region is shaded (with a cross-hatch pattern) in the top-left portion of the figure. Its vertices are: 1. The top-left vertex of the large rectangle. 2. The midpoint on the left side of the large rectangle (labeled "中点"). 3. A point on the top horizontal side of the large rectangle. Visually, this point appears to be vertically aligned with the right vertical side of the small rectangle. * **Internal Lines:** * Two diagonal lines are drawn within the "small rectangle" (the bottom-left rectangle), intersecting at its center. * **Labels and Annotations:** * "中点" (midpoint) is explicitly labeled next to the midpoint on the left side of the large rectangle. * **Relationships and Values:** * The area of the "大长方形" (large rectangle) is given as 60 square centimeters. * The area of the "小长方形" (small rectangle) is given as 40 square centimeters. * The task is to find the area of the "阴影三角形" (shaded triangle).