Question

The supplement of an angle is one of third of its. The measure of the angle

Answer 1

Let the angle be x
Supplement of angle x is (180 − x)° 
Given x = 1/3 ×  (180 − x)° 
⇒ 3x =  (180 − x)° 
⇒ 4x =  180° 
∴ x = 45°
Thus the angle is 45°.

Answer 2

$x +( 1 \div 3)x = 180 \\ 4 \div 3x = 180 \\ x = 180 \times 3 \div 4 \\ x = 135 \\ 1 \div 3 \times x = 45$