Problem 1. Consider the relational database described in Problem 1. Give expressions in tuple relational calculus and domain relational calculus for each of the following queries:
(a) Find the names of all employees who work for company C2 and earn more than $70,000 annually.
(b) Find the names of all employees who are not managers.
(c) Find all the companies that have offices in all the cities in which company C2 has an office.