180 ÷3 = 60 ° (angles on a straight line equals to 180 ° )
a+b+60 =180°
a+ b= 180 ° - 60° = 120°
(a+b) are 2 variables
so 120 ÷2 =60 °
therefore a and b =60 °
c +b+ 60° = 180° ( co - interior angles are supplementary angles )
c+60° +60° =180°
c +120° =180°
c =180°-120°
c=60 °
d=60° (alternate angles are equal )
or
c+b+d=180°
60° +60° + d = 180°
d=180°-120°
d=60°
