Answer:
x=17
Step-by-step explanation
i just did the exact same question on a test and got it right .
5x + 20 = 90 - a = 90 - (3x + 40)
5x + 20 = 90 - 3x - 40 = 50 - 3x
5x + 3x = 50 - 20
8x = 30
x = 30/8 = 15/4
b = 3(15/4) + 40 = 45/4 + 40 = 51.25
The measure of a supplementary angle is 180 - 51.25 = 128.75
It is 6 was not multiplied by 3
The answer should be 6(m+3)= 6m+ 18