How Do You Measure Any Compex Electric Circuits?

I know there are KVL and KVC, which Kirchhoff's laws of current and voltage. This might come in handy, but this isn't obvious in cases like

    5Ω             9Ω
__www__ __www__
|               |                |
|+            z                |
25v         z4Ω           |
|-             z                |
|________|_________|

If we add letters to it to ease the search:

A_______B_______C
|               |              |
|               |              |
|               |              |
D_______E_______F

The question is, what current streams in BE? Which in CF? What voltage is on AB, and what voltage has ED?

So, how do you calculate it? Which methods do you usually use for it?