Statement Justification

line BC is parallel to line ED Given

m∠ABC = 70° Given

m∠CED = 30° Given

m∠ABC = m∠BED Corresponding Angles Theorem

m∠BEC + m∠CED = m∠BED Angle Addition Postulate

(missing)

m∠BEC = 40° Subtraction Property of Equality

A. m∠BEC + 30° = 70°; Substitution Property of Equality

B. m∠BEC + 30° = 70°; Addition Property of Equality

The correct option is A. m∠BEC + 30° = 70°; Substitution Property of Equality.

Step-by-step explanation:

Consider the provided information.

line BC is parallel to line ED: Given

m∠ABC = 70° : Given

m∠CED = 30° : Given

m∠ABC = m∠BED Corresponding Angles Theorem

m∠BEC + m∠CED = m∠BED Angle Addition Postulate

m∠BEC + 30° = 70° Substitution Property of Equality

m∠BEC = 40° Subtraction Property of Equality.

We substitute the value of m∠CED=30° that is why it is know as substitution property of equality.

Hence, the correct option is A. m∠BEC + 30° = 70°; Substitution Property of Equality.