Answer:
45°
Explanation:
The angle with measure of 9x and the angle with measure of 3x are supplementary
9x + 3x = 180°
12x = 180 divide both sides by 12
x = 15
The angle with measure of 9x and angle a are supplementary as well
9x + a = 180
9×15 + a = 180
135 + a = 180 subtract 135 ftom both sides
a = 45°