Geometry

Question Analysis:
This question involves applying CPCTC to set up and solve an algebraic equation for the length of a side of a triangle.
The main focus is on using the fact that corresponding sides of congruent triangles are equal.

Key Concept Explanation:
Since △PQR ≅ △STU, the corresponding sides are equal.
In this case, side QR corresponds to side TU, so we can set up an equation based on their lengths.

Step - by - Step Solution:
1. Set up the equation based on CPCTC:
  - Since QR = TU, we have .
2. Solve for :
  - Subtract from both sides: .
  - This simplifies to .
  - Add 5 to both sides: .
  - We get .
  - Divide both sides by 2:

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