How to create new dependent columns?

[urazbekov]

Dear Community,

I have a problem with construction two new columns which are dependent to each other. A small example below:

time                    Column A,                                    Column B,      Column C

1                    100 (given as variable))                     3                    sum(Column A, Column B)

2                    Column C (of time 1)                        4                    sum(Column A, Column B)

3                    Column C (of time 2)                        5                    sum(Column A, Column B)

4                    Column C (of time 3)                        6                    sum(Column A, Column B)

When I make Column A first, I get message "Column C doesn't exist".

When I make Column C first, I get message "Column A doesn't exist".

It happens because these two columns dependent.

What should I write in script to have them together?

Thank you in advance!