( '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° .
