Answer the following with relational algebra.

a. For each project, list the project name and the total hours per week (by all employees) spent on that project.

b. Retrieve the names of all employees who work on every project.

c. Retrieve the names of all employees who do not work on any project.

DEPARTMENT DEPT_LOCATIO PROJECT \begin{tabular}{|l|l|} \hline Pname & Pnu \\ \hline \end{tabular} WORKS_ON DEPENDENT