Geometry

Question Analysis:  
This question involves identifying how one equality is replaced with another in a logical proof.  
The main focus is on recognizing the use of substitution in mathematical reasoning.  

Key Concept Explanation:  
- The Substitution Property of Equality states that if , then can be replaced with in any equation or expression.  
- Here, allows us to replace with in the equation .  

Step-by-Step Solution:  
1. Given (Statement 1).  
2. Given (Statement 2).  
3. Since , we substitute in place of in Statement 2: