Question #1
Find all single female employees
SELECT NationalIDNumber, MaritalStatus, Gender FROM HumanResources.Employee WHERE MaritalStatus = 'S' AND Gender = 'F'
Question #2
Find all employees that have 40 to 80 hours of vacation time.
SELECT NationalIDNumber, MaritalStatus, Gender, VacationHours FROM HumanResources.Employee WHERE VacationHours >= 40 AND VacationHours <= 80
Question #3
Find all employees that have 40 to 80 hours of vacation time or 40 to 80 hours of sick time, and are male.
SELECT NationalIDNumber, MaritalStatus, Gender, VacationHours, SickLeaveHours FROM HumanResources.Employee WHERE ( (VacationHours >= 40 AND VacationHours <= 80) OR (SickLeaveHours >= 40 AND SickLeaveHours <= 80) ) AND Gender = 'M'
Notice on this last example we used parenthesis to ensure the order of evaluating the clauses was correct.