What do you think is the best move on this board? Assume you can have any piece.
I usually place a different knight on c7 which forces the king to move or lose the queen. Then, I take the rook. If black takes the other knight, I place a pawn on c7 forking the knight and queen.
Take a look:
In my ideal plan you would give up 2 knights for a knight and a rook and gain a promoted queen.
So in your math
Losses:
Gains: