What is the missing step in the given proof?
a.
statement: m∠4 = m∠15
reason: substitution property of equality
b.
statement: m∠4 + m∠8 = 180°
reason: definition of supplementary angles
c.
statement: ∠7 and ∠8 are supplementary.
reason: linear pair theorem
d.
statement: m∠4 = m∠16
reason: transitive property of equality
e.
statement: ∠15 and ∠8 are supplementary.
reason: transitive property of equality