Supplementary angles are two angles that add up to 180 degrees. Given that one angle is 30°, you can find the measure of angle \( x \) using the following equation:
\[ x + 30° = 180° \]
To find \( x \), subtract 30° from both sides:
\[ x = 180° - 30° \] \[ x = 150° \]
Thus, the measure of angle \( x \) is \( 150° \).