How to reuse calculated columns avoiding duplicating the sql statement?

I have a lots of calculated columns and they keep repeting themselves, one inside of the others, including nested cases statements.

There is a really simplified version of something that i've searching a way to do.

SELECT 
    (1+2) AS A, 
    A + 3 AS B, 
    B * 7 AS C 
FROM MYTABLE

Thanks in advance.