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