Firstly, we need to find m<BCA
<BCA+<BCD=180°
m<BCD=111°
<BCA+111°=180°
m<BCA=69°
Secondly, we need to find y
The sum of all angles of triangle is equal to 180°, so
[tex]4y + 3y + 6 + 69 = 180 \\ 7y = 105 \\ y = 15[/tex]
Now we can find m<B
m<B=(3y+6)°
y=15
m<B=3×15+6=51°
Answer: m<B=51°
