A 90° turn to the right from north will point the aircraft east, which is 90° on the compass.
A 270° turn to the right from 90° results in a heading of 360° - 90° = 270° + 90° = 360° = 180°.
A left turn of 90° from 330° results in a new heading of 240°.
A 180° turn from west (270°) will direct the aircraft to the east, which is 90° on the compass.
Northeast corresponds to 45° on the compass.
A 45° left turn from 180° results in a new heading of 135°.
The opposite heading is found by adding or subtracting 180°. 120° + 180° = 300°.