Sum forumla, sum 2 cells then copy down

[FelixSall]

Hi,

Need help to write a formula which can add 2 cells then divide the sum and post in twice, and also add the next row of cells +1 cell step down.
There is probably an easy solution, just dont see it atm .. :/

I'll post a pic of what I mean.

Appreciate any help with this

 

[FelixSall]

https://imgur.com/6BroHYp

 

[Fluff]

How about

Excel 2013/2016
	M
2	-12998.1
3	225.52
4	-1700.98
5	1395.62
6	4294.75
7	4294.75
8
9	6386.29
10	6386.29
11	152.68
12	152.68
13	-4294.75
14	-4294.75
Input

Cell Formulas
Range	Formula
M9	=IF(MOD(ROW(),2),AVERAGE(OFFSET($M$2,ROW()-ROW(M$9),0,2))*-1,M8)