How can I perform arithmetic operation from 2 difference sources?

Is there a simple way to do addition between 2 different sources. I did 2 queries as shown down below and somehow I’d like to add both SELECT last(“df_complex.used”) FROM “mnt-MediaPool-Media-Movies” and SELECT last(“df_complex.used”) FROM “mnt-MediaPool-Media-TVShows”

    > select * from "mnt-MediaPool-Media-Movies" LIMIT 1
    name: mnt-MediaPool-Media-Movies
    time                df_complex.free df_complex.reserved df_complex.used host          resource
    ----                --------------- ------------------- --------------- ----          --------
    1598650165000000000 2743866245120   0                   475488329728    truenas_local df
    > select * from "mnt-MediaPool-Media-TVShows" LIMIT 1
    name: mnt-MediaPool-Media-TVShows
    time                df_complex.free df_complex.reserved df_complex.used host          resource
    ----                --------------- ------------------- --------------- ----          --------
    1598650165000000000 2743866245120   0                   529429798912    truenas_local df

In Grafana, I know that I can do simple addition operation query like this from the same source but not with 2 or more different sources. Is there a way or I have to add variable for each different source? Thanks in advance

SELECT last("df_complex.free") + last("df_complex.used") FROM "mnt-MediaPool-Media-Movies"