#### Answer

a) Given
b) Definition of midpoint
c) Substitution Property
d) $2x=12$
e) Division Property of Equality

#### Work Step by Step

a) The starting point of a proof is given.
b) The segments on either side of the midpoint are congruent by definition.
c) The Substitution Property allows us to substitute for one term with another term that is equal to it.
d) Each side is divided by 2.