One third of its supplementary angle is

A
$135 °$
B
$45 °$
C
$130 °$
D
$60 °$

Solution:

$\begin{array}{l} x + \frac{x}{3} = 180 ° \\ 3 x + x = 540 ° \\ 4 x = 540 ° \\ x = \frac{540 °}{4} \\ x = 135 ° \\ \frac{x}{3} = \frac{135 °}{3} = 45 ° \end{array}$

Solution:

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