Hours Calculation

Hi Expert, I have four columns of hours of  time clock in my page and I want to add a new column, which will calculate the total hours of the day. I calculatede the time from EXCEL every time, but how to accomplish it in VB.net in the web pape?  Appreciate it!
 
Clock-in(1)  Clock-out(1)  Clock-in(2)  Clock-out(2)  Total
8:30AM         12:00PM    1:00PM     5:30PM
...