An angle is equal to one fifth of its supplement. What is the measure of that angle?

Let the angle be 𝑥.
The supplement of an angle is the angle that, when added to the given angle, equals 180 degrees. Therefore, the supplement of the angle is (180 - 𝑥) degrees.
According to the problem, the angle is equal to one-fifth of its supplement, so we can set up the equation:
\( 𝑥=\frac{\mathrm{1} }{\mathrm{5}}(180-𝑥) \)
Multiplying both sides by 5 to eliminate the fraction gives:
5𝑥 = 180−𝑥
Adding 𝑥 to both sides results in:
𝑥 + 5𝑥 = 180
6𝑥 = 180
Now, divide both sides by 6:
𝑥 = 30