Answer:
x = 17.5 mm
Step-by-step explanation:
Supplementary means that two angles adds up to 180 degrees.
If C and D are supplementary, that means that they equal to 180 degrees.
Combine like terms: 6x - 4 + 4 + 4x + 9 - 9 = 180 + 4 - 9
10x / 10 = 175 / 10
x = 17.5
So, x = 17.5 mm
