Extend line AB to meet line PR at point G.
Given: PQ || AB,
∠QPR = ∠BGR =102° [Corresponding angles of parallel lines are equal] And PR || BC,
∠RGB+ ∠CBG =180° [Corresponding angles are supplementary]
∠CBG = 180° – 102° = 78°
Since, ∠CBG = ∠ABC
∠ABC = 78°