Find the value of ∠CAB if PQ || RS and AB ⊥ RS.

Given, AB ⊥ RS 

⇒ ∠ABC = 90°
Since line PQ || RS and AB are transversal, ∠QAB = ∠ABC = 90°. (Alternate Interior Angles)
Since line PQ || RS and AC are transversal, ∠RCA = ∠QAC = 135°...(Alternate Interior Angles)
Now, ∠CAB = ∠QAC – ∠QAB
⇒ ∠CAB = 135° – 90°
⇒ ∠CAB = 45°