Anwser : n = -2
Combine Like Terms
Add 4n to both sides
Subtract 3 from both sides
A = n= -2
10A + 5B = 15
-10 -10
---------------------
A + 5B = 5
So::
A + 5B = 5
-5 -5
-----------------
A + B = 0
That should be your answer.
The answer I believe is D. BC is congruent to DF