Morgan starts with 4k bookmarks and Tracey starts with 3k bookmarks
Morgen give half of hers to Tracey so now Morgan has 2k bookmarks and Tracey has 5k bookmarks
BUT morgen has 9 more than Tracey which means that Mogen must have 5k-9 bookmarks
So Tracy has 2k bookmarks which is also 5k-9 bookmarks
which means that
2k=5k-9
Once you find k substitute it back to fin how many bookmarks Morgan started with.