Substraction from 2 Fields, out of two .csv Files

Question

Hello all,
i got help by Vulpes in this Thread-> 

http://www.c-sharpcorner.com/Forums/Thread/205494/string-split-how-to-calculate-slot.aspx  

I wanna rewrite the Code from Vulpes, but dont now how to do that with two files.

I have a FIRST File that looks like that: (crap Export i made)

"";"";0
"  09000";"Catalog 1";10148
"  09001";"Catalog 2";20
"  09002";"Catalog 3";166

I have a SECOND File that looks like that:
"  09000";476
"  09001";10
"  09005";5

What to do? the Output file must look like that:
09000~Catalog 1~9672
09001~Catalog 2~10
09002~Catalog 3~161

I need to substract Field 3 from the FIRST File, with Field 2 from the SECOND File and get a Output like above.