The sum of measures of angles of a triangle is always 180°, so you have
... (2x)° + (3x)° + (x+30)° = 180°
... 6x + 30 = 180 . . . . . . . . . . . . . collect terms
... 6x = 150 . . . . . . . . . . . . . . . . . subtract 30
... x = 150/6 = 25 . . . . . . . . . . . . divide by 6
The appropriate choice is
... B 25