Find the missing angle measures by examining the angle relationships first

m m m

∠ b = 43° — — { Vertical opp. angles]

Now, see 43 and a are together compromising the linear pair so,

= 43 + a = 180°

= a = 180 - 43

= a = 137

Like b, similarly here also a = c = 137° {Vertical opp. angles}