#### Answer

a) Given
b) Segment Addition Postulate
c) Substitution
d) Adddition property
e) Subtraction property of equality
f) Division property of equality

#### Work Step by Step

a) This equation was stated in the problem.
b) The length of two adjacent segments sums to the length of the segment they comprise.
c) The given values were substituted.
d) The addition property allows us to combine like terms.
e) 3 was subtracted from each side.
f) Each side was divided by 3.