please answer #7 <3
tysm
if u can explain why i’ll give u brainlist

Answer:
BC=2
Step-by-step explanation:
The equation is
AB+BC+CD=21
7+BC+12=21
19+BC=21
BC=21-19
BC=2
Answer:
Bc = 2
Step-by-step explanation:
Just add AB + CD
you'll get 19
substract it from AD
21 - 19 = 2
In Above question b = 39°
Not 31