Answer:
a = 84°
Explanation:
∠ QPR and ∠ TPR are adjacent and supplementary, thus
∠TPR = 180° - 123° = 57°
Given there are parallel lines , then
∠ PTR = 27° ( alternate angle )
The external angle of a triangle is equal to the sum of the 2 opposite interior angles.
∠ TRS is an external angle , thus
∠ TRS = a = 57° + 27° = 84°