Answer: 45°
Explanation:
Let the angle be x and its complement be y
Also,
Complement = 1/3 × Supplement
So, 
Supplement = 3 × Complement
 = 3y
According to Question:
I. x + y = 90° -----(1)
II. x + 3y = 180° -----(2)
 On subtracting eq (1) from (2) we get
 2y=90°
  y=45°
Now, From eq (1)
 x + y = 90° 
 x = 90° - 45°
 x = 45°
∴ The angle is 45°