Answer:
C. 120 deg
Step-by-step explanation:
All sides of a rhombus are congruent.
That means that triangle ADC is an isosceles triangle with AD = CD, so angles DAE and DCE are congruent.
m<DAE + m<DCE + m<ADC = 180
30 + 30 + m<ADC = 180
m<ADC = 120
Opposite angles of a rhombus are congruent, so
m<ABC = m<ADC = 120
