Except as provided in subsection (b) of this section, each contractor and subcontractor under a public work contract shall pay not less than the prevailing wage rate of straight time to an employee for each hour that the employee works. A contractor and subcontractor shall pay an employee the prevailing wage rate of overtime for each hour that the employee works: in excess of 10 hours in any single calendar day; in excess of 40 hours per each workweek; or on Sunday or a legal holiday.