Geometry

Question Analysis:
This question tests the ability to determine the length of a corresponding side in congruent triangles.

Key Concept Explanation:
Corresponding sides of congruent triangles are equal in length, and the naming order indicates which sides correspond.

Step-by-Step Solution:
Given ⊿PQR ≅ ⊿STU, the vertex correspondence is:
P ↔ S, Q ↔ T, R ↔ U.
Therefore:
PQ corresponds to ST.
QR corresponds to TU.
PR corresponds to SU.
Since PR = 6 cm, SU must also be 6 cm.

Option Analysis:
A: Incorrect (length of QR, not PR).
B: Correct (SU corresponds to PR).