Calculations using Time

Hi

I am trying to find out how to do some basic calculations using time ( i.e. hh:mm:ss).
I have a sheet which shows the number of hours spent on a task each day which I need to add up to get a total for a month in hh:mm:ss format. I have found you can do this by setting the format of the cell where you add up the totals to [h]:mm:ss format. This works quite happily and gives you a total hours worked on that task for the month.

What I now want to do though is display this as a % of the total hours in the month spent on all tasks. So say you worked X days this month and you know each day was 9 hours long. X is a variable number say in Cell A1. You would have a formula to work out the total worked hours (9*A1) . However I can't quite find a way to calcualte this correctly in [h]:mm:ss equivalent format. I need to then divide the total hours worked on my task by this figure and display as a %. i.e what % of the total hours worked this month were spent on this task.

I am really struggling to work out a formula that can calculate the total hours for X days in the equivalent of [h]:mm:ss format and produce a correct result as a percentage.

Any bright sparks out there know how to do this?

Many Thanks