Explanation
Two line segments are congruent if they have the same length.
That is by CPCT rule, corresponding parts of congruent triangles are equal.
Then, PQ=ST, QR=TU, PR=SU, ∠P=∠S, ∠Q=∠T and ∠R=∠U.
Thus, QR=TU.
∴TU=6 cm.
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