P$7.$ Consider the network fragment shown below. x has only two attached neighbors, w and y$.$ w

has a minimum$-$cost path to destination u $($not shown$)$ of $5,$ and y has a minimum$-$cost path to u

of $6.$ The complete paths from w and y to u $($and between w and y$)$ are not shown. All link costs

in the network have strictly positive integer values.