[MiNT] counting up in bash

[milarb@volny.cz (Bohdan Milar)]

Hi all,

I write some bash scripts and need to do some calculations. For example I have 
a file containing the 3 following lines:

15
25
20

I need to have the number 60, as their sum, in some variable. How should I do 
that? Could somebody tell me which tool and how to use?

Regards,

Bohdan