Please, post the entire query.

From what I could understand from your post you could use a subquery or a derived table.

E.g.:

selectC = derived_table_B.B + derived_table_B.A

from(

selectB = derived_table_A.A + 1

,derived_table_A.A as A

from(

selectA = 2 + 3

) derived_table_A

) derived_table_B