Macro for summing every other column and placing the each sum at the row 51

[Pandrade]

Hello,
I am working on a worksheet with thousands of columns. The columns alternate between salary and quantity. I need to place the sum total for each salary column on row 51 and the average for each salary column will be calculated by dividing the sum of each salary by the number of salaries found on row 50, for each salary column (they start at column L). The average will be placed on row 52 for each salary column (every other column). Here is a picture for clarity:

 

[Fluff]

Duplicate How to copy a formula to every other column
Please do not post the same question multiple times. All clarifications, follow-ups, and bumps should be posted back to the original thread.
Per forum rules, posts of a duplicate nature will be locked or deleted (rule 12 here: Forum Rules).