Extracting daily data from a 7 day rolling report that is delievered daily

Hello all,

Here is an interesting one. I am receiving a 7 day rolling report daily and need to find out what teh daily figure is. Hard to get your head around - so will explain another way every day, I receive a report that shows me the last 7 days of data aggregated - but no read out on what the number was yesterday. But becuase it is updated daily, I *Should* be able to get the daily figure form this data - but its not easy.....

I've set up a simulated scenario - if anyone can help me, it would be fatnastic!

See below (and attached with formulas) - the column simulated daily data is daily data (and the desired solution); the simulated 7 day rolling column is a sum of the last 7 days (for Day 7, its a sum of daily data from days 1-7). I need to be able to work out the aily data based ONLY on the data from the simulated 7 day rolling.

Day simulated daily data simulated 7 day rolling
Day 1 1
Day 2 2
Day 3 3
Day 4 4
Day 5 5
Day 6 6
Day 7 7 28
Day 8 8 35
Day 9 9 42
Day 10 10 49
Day 11 11 56
Day 12 12 63
Day 13 13 70
Day 14 14 77
Day 15 15 84
Day 16 16 91
Day 17 17 98
Day 18 18 105
Day 19 19 112
Day 20 20 119
Day 21 21 126
Day 22 22 133
Day 23 23 140

Any thoughts would be greatly appreciated.