According to question
∠1 + ∠2 + ∠3 + ∠4 = 360° (Angles formed at a point is 360°)
But ∠1 + ∠2 + ∠3 = 230° (given)
(∠1 + ∠2 + ∠3) + ∠4 = 360°
230° + ∠4 = 360°
∠4 = 360° – 230°
∠4 = 130°
But ∠1 + ∠4 = 180° (linear pair axiom)
∠1 + 130°= 180°
∠1 = 180°- 130° = 50°