Given the following schema where primary keys are underlined and foreign keys are marked with #, express in Relational Algebra the queries below: Employee (employeeNo, empName, jobTitle) Project (projectID, projectName, sponsor, startYear, endYear) WorkedOn (#employeeNo, #projectID, year, month, noHours) a) List the Ids and names of projects, which are sponsored by "Petrofac" and finished before 2021. [1 mark] b) List the numbers of employees (employeeNo) who worked on projects in 2020. [1 mark] c) List the name of the projects on which employees spent more than 500 hours. [1 mark]