What is the reason for statement 4 in this proof?

Transitive Property of Equality
definition of midpoint
definition of parallel lines
Reflexive Property of Equality

What is the reason for statement 4 in this proof Transitive Property of Equality definition of midpoint definition of parallel lines Reflexive Property of Equal class=
What is the reason for statement 4 in this proof Transitive Property of Equality definition of midpoint definition of parallel lines Reflexive Property of Equal class=