7. Consider the following relations for a database that keeps track of business trips of salespersons in a sales office: SALESPERSON(Ssn, Name, Start_year, Dept_no) TRIP(Ssn, From_city, To_city, Departure_date, Return_date, Trip_id) EXPENSE(Trip_id, Account\#, Amount) A trip can be charged to one or more accounts. Specify the foreign keys for this schema, stating any assumptions you make. 8. Consider two relations R1(A,B) with the tuples (1,5),(3,7) and R2(A,C)= (1,7),(4,9). Assume that R(A,B,C) is the full natural outer join of R1 and