Excellent job! Looks much better than mine too!!
Some minor adjustments:
The PK for Ticket Response is ( Ticket Number, Ticket Response ID ) (in that order). Yes, a PK can have more than attribute / column in it. Ticket Number is also a FK (points to a "parent" table with that attribute as a unique key). Ticket Response ID is not a FK, just part of the PK.
Similarly for Ticket Cancellation, PK will be ( Ticket Number, Ticket Cancellation ID ).
SQL DBA,SQL Server MVP(07, 08, 09) A socialist is someone who give you the shirt off *someone else's* back.