Consider the following table definition, where the primary keys are underlined. Give an expression in relational algebra for each of the following queries.

Athlete (aID integer, aName string, ranking integer, age integer)

Event (eID string, eName string, eLocation string)

Competes (aID integer, eID string, sport string, year integer)

7. Find the aID of athletes over the age of 19 who have competed in XGames.