Answer:
B)140
Step-by-step explanation:
So a line is=180 and the interior angles of a triangle= 180, so I did some manipulations
1. 100 + (5x+5) + <ECD = 180. But we also know that (21x-7) + <ECD=180. With some manipulation we can find that <ECD= 180 - (21x-7), so we can plug that into the other equation
2. Now: 100 + (5x+5) + (180- (21x-7))= 180
3. Solve:
105+5x+180-21x+7=180
112-16x=0
112=16x
x=7
4. Plug x=7 into 21x-7= 140
