Answer:
89 degrees
Step-by-step explanation:
supplementary angles add up to 180 degrees, so we can add up A and B and make it equal to 180.
(x-18)+(x-20)=180
2x-38=180
2x=218
x=109
then, we plug in 109 for x in the mB equation.
mB=x-20
mB=109-20
mB=89 degrees
therefore, the measure of B is 89 degrees.
