Answer:
Step-by-step explanation:
60+b+d=180 (angles on a st. line)
∠d=∠a (alternate interior angles)
60+∠b+∠a=180 (substituting)
60+∠b+2∠b=180
3∠b=180-60=120
∠b=140/3=40°
a=2b=2×40=80°
a+c=180
80+c=180
∠c=180-80=100°
∠d=∠a=80°
