A. Given the following database schema E- Employee (Ename, SSN, Age, salary, Supervisor_SSN, Dno) D - Department (Dname, Dnumber, Dlocation, Manager_SSN, Mgr_StartingDate) P - Project (Pname, Pnumber, Plocation) W- Works_On (ESSN, Pno, Hours) De - Dependent (ESSN, D name, DOB, Relationship) and the following set of foreign keys: Employee.Supervisor_SSN Employee.SSN Employee.Dno Department.Dnumber Department. Manager_SSN Employee.SSN Works_ON.ESSN Employee.SSN Works_On.Pno Project.Pnumber Dependent.ESSN Employee.SSN Write the following queries in relational algebra: a. Find the names of all employees who work on any project; b. Find the names of all employees who work more than 15 hours on project X (Pname)