Iseriously can't do this type of questions so can someone solve it detailedly and putting with letters (there is a system you name conducting wires as a, b etc. i don't know what that system calls in physics)find the equivalent resistance with details

4 Ohms

Explanation

(This is seriously not as hard as it looks :)

You only need two types of calculations:

I am attaching a drawing showing the process of stepwise replacement of two resistances at a time (am using rectangles to represent a resistance). The left-most image shows the starting point, just a little bit "warped" to see it better. The two resistances (6 Ohm next to each other) are in parallel and are replaced by a single resistance (3 Ohm, see formula above) in the top middle image. Next, the two resistances (9 and 3 Ohm) are nicely in series, so they can be replaced by their sum, which is what happened going to the top right image. Finally we have two resistances in parallel and they can be replaced by a single, final, resistance as shown in the bottom right image. That (4 Ohms) is the equivalent resistance of the original circuit.

Using these two transformations you will be able to solve step by step any  problem like this, no matter how complex.  

+15-35=-20

going in opposite directions