请用小学三年级的知识讲解这道题目的解法---**Extracted Content:** **Question Stem:** 【Act 4】 A square piece of glass had 3 cm cut off from each side to form a smaller square. The area of the cut-off part is 63 cm². What is the side length of the original square? **Other Relevant Text:** * 3 cm (labeled along the top edge of the cut-off area) * 3 cm (labeled along the right edge of the cut-off area) * 63 cm² (labeled within the cut-off area) **Options:** (No options are provided in the image) **Chart/Diagram Description:** * **Type:** Geometric diagram illustrating squares and a cut-off region. * **Main Elements:** * Two concentric squares are implied, representing the original square and a smaller square inside it. * The region between the two squares is highlighted in a darker color (yellow/orange), representing the "cut-off part". * The cut-off part is an L-shaped region surrounding the inner square. * Dashed lines indicate the boundaries of the inner, smaller square. * Labels show dimensions: "3 cm" is labeled vertically along the right edge of the cut-off area, and "3 cm" is labeled horizontally along the top edge of the cut-off area. These labels indicate the width of the cut-off strip. * The area of the highlighted L-shaped cut-off region is labeled as "63 cm²". * The diagram visually represents a larger square from which a uniform strip of 3 cm width is removed from two adjacent sides (top and right in this orientation) and the resulting L-shaped area is 63 cm². Implicitly, a strip is removed from all four sides to form the inner square. The diagram shows a section of this, indicating the 3 cm width of the cut off strip and its area.