Specify the following queries on the given database schema using relational algebra.

a$)$ Retrieve the SSNs and names $($Lname$,$ Fname$)$ of all employees in department $4$ who work more than $5$ hours per week on both 'ProductX' and 'ProductY' projects.

b$)$ List the SSNs and names of employees who have no dependents.

c$)$ Find the SSNs and names of employees who are directly supervised by a supervisor who is directly supervised by 'James Borg'.

d$)$ Retrieve the SSNs and names of employees who work on at least one project.

e$)$ Retrieve the SSNs and names of employees who work on every project located in Stafford.

f$)$ Retrieve the name of the department with Dnumber $=5,$ and the lowest salary of the male employees who work in that department.

g$)$ Retrieve the highest salary of all employees $($the SSNs and names $($Lname$,$ Fname$))$ who work in the department with Dnumber $=4.$

h$)$ Find the SSNs$,$ names $($Lname$,$ Fname$)$ and addresses of employees who work on at least one project located in Houston and whose department has a location in Houston.

i$)$ List the SSNs and last names of department managers who have the spouse as the dependent.