calculate hrs

Hi
i have two webforms .In webform1 i have starttime and endtime  to enter
In webform2 i have starttime and endtme design something like below
starttime endtime          bf     lunch      dinner   total
7:00AM   10:00AM        15                               02:45:00
10:15AM    12:00PM             30                        01:15:00
12:30PM  5:00PM        &nbs ...