Something like this (be sure to format column C as h:mm)?
<TABLE style="BACKGROUND-COLOR: #ffffff; PADDING-LEFT: 2pt; PADDING-RIGHT: 2pt; FONT-FAMILY: Calibri,Arial; FONT-SIZE: 11pt" border=1 cellSpacing=0 cellPadding=0><COLGROUP><COL style="WIDTH: 30px; FONT-WEIGHT: bold"><COL style="WIDTH: 64px"><COL style="WIDTH: 64px"><COL style="WIDTH: 64px"></COLGROUP><TBODY><TR style="TEXT-ALIGN: center; BACKGROUND-COLOR: #cacaca; FONT-SIZE: 8pt; FONT-WEIGHT: bold"><TD></TD><TD>A</TD><TD>B</TD><TD>C</TD></TR><TR style="HEIGHT: 18px"><TD style="TEXT-ALIGN: center; BACKGROUND-COLOR: #cacaca; FONT-SIZE: 8pt">3</TD><TD style="TEXT-ALIGN: right">10:30</TD><TD style="TEXT-ALIGN: right">12:00</TD><TD style="TEXT-ALIGN: right">1:30</TD></TR><TR style="HEIGHT: 18px"><TD style="TEXT-ALIGN: center; BACKGROUND-COLOR: #cacaca; FONT-SIZE: 8pt">4</TD><TD style="TEXT-ALIGN: right">12:00</TD><TD style="TEXT-ALIGN: right">12:45</TD><TD style="TEXT-ALIGN: right">0:45</TD></TR><TR style="HEIGHT: 18px"><TD style="TEXT-ALIGN: center; BACKGROUND-COLOR: #cacaca; FONT-SIZE: 8pt">5</TD><TD></TD><TD>Total</TD><TD style="TEXT-ALIGN: right">2:15</TD></TR></TBODY></TABLE>
<TABLE style="BORDER-BOTTOM-STYLE: groove; BORDER-BOTTOM-COLOR: #00ff00; BACKGROUND-COLOR: #fffcf9; BORDER-TOP-COLOR: #00ff00; BORDER-LEFT-STYLE: groove; FONT-FAMILY: Arial; BORDER-TOP-STYLE: groove; COLOR: #000000; BORDER-RIGHT-COLOR: #00ff00; BORDER-RIGHT-STYLE: groove; FONT-SIZE: 10pt; BORDER-LEFT-COLOR: #00ff00"><TBODY><TR><TD>Spreadsheet Formulas</TD></TR><TR><TD><TABLE style="FONT-FAMILY: Arial; FONT-SIZE: 9pt" border=1 cellSpacing=0 cellPadding=2><TBODY><TR style="BACKGROUND-COLOR: #cacaca; FONT-SIZE: 10pt"><TD>Cell</TD><TD>Formula</TD></TR><TR><TD>C3</TD><TD>=B3-A3</TD></TR><TR><TD>C4</TD><TD>=B4-A4</TD></TR><TR><TD>C5</TD><TD>=SUM(C3:C4)</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>