Answer:
supplementary, 19
Explanation:
Since both angles measures add up to 180°, therefore they’re called supplementary angles.
To find the value of x, add the two angle measures
123° + 3x° = 180°
reverse the sum
3x° + 123° = 180°
Subtract 123° from both sides
(3x° + 123° - 123° = 180° - 123°)
3x° = 57°
Solve for x
x = 57°/3°
x = 19