Answer:
10 units
Step-by-step explanation:
We are given that
BD=x+29
AD=x+39
AC=20
BC=x+19
AC=AB+BC
20=AB+x+19
AB=20-x-19=1-x
AD=AB+BD
![x+39=1-x+x+29](https://tex.z-dn.net/?f=x%2B39%3D1-x%2Bx%2B29)
![x=30-39=-9](https://tex.z-dn.net/?f=x%3D30-39%3D-9)
Substitute the value of x=-9
Then , we get BC=
units
Answer: BC=10 units
Your answer is B. 12.
12 kids are unaccounted for after you subtract the kids that take A1, then A2, the both subjects.