Answer:
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Use trigonometry.
Since all three sides are known, you may choose either sine, cosine or tangent.
We'll use sine here:
- sine = opposite leg / hypotenuse
- sin ∠R = TS/TR
- sin ∠R = 60/68
- sin ∠R = 0.8823
- m∠R = arcsin 0.8823
- m∠R = 61.92°