Find the general flow pattern of the network. Assuming that the flows are all nonnegative, what is the smallest possible value for $x_4$?
Points of Intersection: Flow In = Flow Out
A: $x_1+x_4 = x_2$
B: $x_2 = x_3 + 100$
C: $x_3 + 80 = x_4$
The total flow in equals the total flow out, so you can set up other equations...
How do I turn this into a solvable matrix to get the answer?