The figure below shows a network of one$-$way streets, together with nodes A$,$ B$,$ C$,$ D and E$.$ There are $70$ cars entering node A from the left, $60$ of them exit through node D to the right, and the remaining $10$ exit through node E to the right. The variables

x

$1$

through

x

$5$

represent the numbers of cars moving along the paths in the network.