Trend and Forecast Data

Hi all,

I have been asked to trend/forecast some data and I am not sure how to work it out in the format of the table I am using. All the tutorials use data going down but mine is going across.
Calls arrive in 15 minute intervals so based on the Mondays so far in the last six weeks I need to know how many calls will drop in those 15 minute intervals. I am not good explaining so I have attached a sheet FYI, I am sure that will explain it better. The highlighted column is where I need the data populating.
Any help will be appreciated.
Regards
Mark