The buyer and seller bargain on a fixed price plus incentive fee contract, the aim cost of the contract is 200000 dollars, the aim profit is 30000 dollars, the aim price is 230000 dollars, the two parties also consult the highest price at 270000 dollars, the halve ratio is 70/30, if the seller accomplished the fact cost is 170000 dollars, how much profit should the buyer pay for the seller?

A、21000

B、35000

C、39000

D、51000