Answer:
140 degrees
Step-by-step explanation:
At this point, we know that opposite angles in quadrilaterals equal 180 degrees. The opposit angles in this particular quadrilateral is D and B
D+B=180
x+(4x-20)=180
5x-20=180
5x=200
x=40
Now, It asks for the measurement of angle B, not what X equals, so we plug it into the equation.
4x-20
4(40)-20
160-20=140
140 degrees
I hope this helped you out and I wish you good luck on the rest!
-Aspen