Answer
m$\angle$B=110$^{\circ}$
Work Step by Step
m$\angle$D+m$\angle$C=180
5x+10+5y+20=180
5y=150-5x
y=30-x
m$\angle$A=m$\angle$C
3x+y=5y+20
3x+(30-x)=5(30-x)+20
2x+30=150-5x+20
7x=140
x=20
y=30-x
y=30-20
y=10
m$\angle$B=m$\angle$D
m$\angle$B=5x+10
m$\angle$B=5(20)+10
m$\angle$B=110$^{\circ}$
