근무시간 계산

안녕하세요.. 인터넷으로 찾아봐도 잘 모르겠습니다. 예를들어     <TABLE class=txc-table style="FONT-SIZE: 9pt; BORDER-TOP: medium none; FONT-FAMILY: ; BORDER-RIGHT: medium none; BORDER-COLLAPSE: collapse; BORDER-BOTTOM: medium none; BORDER-LEFT: medium none" cellSpacing=0 cellPadding=0 width=700 border=0> <TBODY> <TR> <TD style="BORDER-TOP: #000 1px solid; BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; BORDER-LEFT: #000 1px solid; WIDTH: 25%"> 근무시작시간(년,월,일,시간)</TD> <TD style="BORDER-TOP: #000 1px solid; BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> 종료시간(년,월,일,시간)</TD> <TD style="BORDER-TOP: #000 1px solid; BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> 총근무시간</TD> <TD style="BORDER-TOP: #000 1px solid; BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> </TD></TR> <TR> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; BORDER-LEFT: #000 1px solid; WIDTH: 25%"> 2013-10-01 10:10</TD> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> 2013-10-02 10:10</TD> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; TEXT-ALIGN: center; WIDTH: 25%"> ?</TD> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> </TD></TR> <TR> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; BORDER-LEFT: #000 1px solid; WIDTH: 25%"> </TD> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> </TD> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> </TD> <TD style="BORDER-RIGHT: #000 1px solid; BORDER-BOTTOM: #000 1px solid; WIDTH: 25%"> </TD></TR></TBODY></TABLE>   이렇게 총근무 시간을 구하고 싶은데 설정부터 어떻게 해야하는지 가르쳐 주십시요,,, 감사합니다...