substract multiple columns from multiple tables

hey all, 

trying to figure this one out, i have to count for all the unccounted hours. this will look like x=(a-b) - (c-d). i tried to do just that,creating a quick measure for (a-b) then anothe for (c-d) and then another for the formula.. makes no sense, don't laugh i don't know power query. going that route gives me wrong results for whatever reason. 

is there a simpler way in doing that?

and no, i cannot do that in sql, since it comes from totally different databases from different servers ( maybe i can, but i don't know it).

all values(a,b,c,d) are coming from diff tables. value 'a' and 'b' are  measures using calculate function. 'c' and 'd' are columns from 2 different tables. 

Happy Holidays and thank you in advance. 🙂