## Network Flow Diagrams - How do I make cuts like these?

Hey guys - sorry to ask another question, I've looked around but i can't find anything that says anything about these specific cuts =S

The picture below shows part of a system of pipes flowing from Source, S, to Sink, T. The arrows are labelled to show excess capacities and potential backflows. Calculate the capacity of the cut shown by the red line.

How do i do this with potential backflows and excess capacities? =S

Thanks guys =]