def time_worked_for_sub_item(time_sheet, work_item_nm='', sub_work_item_nm=''):
    """
    takes a time_sheet, work item number, and a sub work item number and returns
    the total hours worked for that sub-item
    """
    result = 0.00
    for work_time_obj in time_sheet[work_item_nm][sub_work_item_nm]:
        result += work_time_obj['hoursWorked']
    return result