Answer: The missing step is,
m∠OCP ≅ m∠ABC because corresponding angles made by the same transversal on the parallel lines are congruent.
Step-by-step explanation:
Given :
, 
And, 
We have to Prove : Angle PCQ is complementary to angle ABC
⇒ 
Proof: Since, 
⇒ 
But,
( By angle addition postulate )
⇒
( By transitive property of equality )
Since,
,
⇒
( corresponding angles made by the same transversal are congruent)
⇒
( By the definition of congruent angles )
This leads,
( by the transitive property of equality )
Thus, by the definition of complementary angles,
Angle PCQ is complementary to angle ABC
Hence proved.