Answer: The missing step is,
m∠OCP ≅ m∠ABC because corresponding angles made by the same transversal on the parallel lines are congruent.
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.