Problem $2\mathrm{.}3.(4+4$ points$)$ In each of the following traffic networks con$-$

sisting of one$-$way streets, a number along an edge refers to the number of

cars per hour passing through the street in the indicated direction. For each

network, write down a linear system whose solutions give the possible tuples

of values for the traffic flow $($cars per hour$)$ passing through the unlabelled

edges in the indicated direction in the network. Solve the system and say at

which streets you would place additional counters if you cannot yet deter$-$

mine the flow precisely. Do not place more counters than necessary!