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.