If the supplement of an angle is two-third of itself, then its supplement is

('x' is not 144.)

The supplement of an angle is (180 - x).

The problem says that (2/3) of 'x' is equal to (180 - x).

180 - x = 2/3 x

Multiply each side by 3:

(Note: 3 x 180 = 540.)

540 - 3x = 2x

Add 3x to each side:

540 = 5x

Divide each side by 5:

x = 108°.