$7,000 is correct but I don't like the way you got there.
You start with an $8,000 loss from Company C. You subtract from that $8,000 of the $10,000 loss on Company B (always apply non-discount gains to losses first). You then have a residual $2,000 of non-discount gain plus $10,000 of discount gain from Company A. Applying the discount to the latter you have $2,000 + $5,000 = $7,000.
