Sick leave annual leave minutes spreadsheet

My computer has Excel 2003... When employees turn in their time for sick or annual leave, they will put down a number such as:
7:45 (7hrs 45min)
Or
7.45
...I need a way to enter that on my spread sheet as time, but not am or pm time. And not a 24 hour time. I have to subtract it from their balance of hours and add in any new time accrued. Numbers sometime look like: 156.79 which should be 157 hrs 19 mins.

I will appreciate any help that I can get!

The top of my spreadsheet has these headings:

Earned, Sick Leave Taken, Balance

It is Excel 2003/// I am a newbie...

Carryover From Previous Year 102.20 Carryover from Previous Year: 25.45
ANNUAL LEAVE SICK LEAVE
Month Earned Taken Balance Earned Taken Balance
July 12.10 40.00 74.30 10.00 2.00 318.45
August 12.10 86.40 10.00 10.00 318.45
Sept 12.10 98.20 10.00 22.00 306.45
October 12.10 8.00 102.30 10.00 5.00 311.45
Nov 12.10 16.00 98.40 10.00 8.00 313.45
Dec 12.10 32.00 78.50 10.00 5.30 318.15
January 12.10 91.30 10.00 17.00 311.15
February 12.10 103.40 10.00 29.30 291.45
March 12.10 16.00 99.50 10.00 5.00 296.45
April 12.10 16.00 96.00 10.00 8.00 298.45
May 12.10 8.00 100.10 10.00 16.00 292.45
June