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

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 given information, the angle is equal to one-fifth of its supplement. Mathematically, we can express this as: The sum of supplement angles is 180. Let 𝑥 be that angle. Therefore:
𝑥 + 5𝑥 = 180
6𝑥 = 180, divide both sides by 6.
𝑥 = 30