Note:the question should be "sum of the greatest and least AMONG THESE ANGLES is-"
Let us take the angles as 2x, 3x and 5x
Greatest angle will be 5x and smallest will be 2x
Therefore, 2x+5x = 150°
7x = 150°
x = 21.4°
The angles are 2x = 42.8°, 3x = 64.2° and 5x = 107°
4th angle will be : 360° - (42.8° + 64.2° + 107°)
Answer is that the fourth angle will be equal to 146°
Hope this helps :)