Two angles are supplementary if their measures add up to 180 degrees.
Given that one angle measures 122°, we can find the measure of angle X as follows:
\[ X + 122° = 180° \]
To solve for X, we subtract 122° from both sides:
\[ X = 180° - 122° \]
Calculating the right side gives:
\[ X = 58° \]
Therefore, the measure of angle \( _x \) is:
\[ x = 58° \]