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