GDP simple question got me confused: the sale of a capital asset a) Delta Air Lines buys a new jet from Boeing for 200 million dollars.

b) Delta Air Lines sells **one of its jets to Kim Kardashian for 100 million dollars. 

So..

a) $200 million investment, purchase of the final good, so GDP increased by 200 M

b) No change, but why? Even if the had bought the plane for 50 million and made profit by selling it to Kim? Here's my in length answer I am not too certain of:

Does not change. Why? This good was already included in GDP. It was produced and sold. It has not been modified by Delta Air Lines, thus absolutely no value added to this plane.  It is simply the ownership transfer of a good that was bought. However...Wasn't that a service? I mean, Delta made it EASIER for Kim to buy a plane. They provided a service, so a profit would be added to GDP...NO?
No, the sale of a capital asset doesn’t count in GDP, as the cost of the asset was already accounted for when the plane was first sold to Delta. To your second point, if a broker somehow provided a service by facilitating the sale, that would count towards GDP, but the sale itself would not.