The net amount of consideration given by B is £100,000 (that is, the £1m given to A less the £900,000 received from C).
Swm net y gydnabyddiaeth a roddir gan B yw £100,000 (hynny yw, y £1 miliwn a roddwyd i A llai'r £900,000 a dderbyniwyd gan C).