$2$ Telephone calls from New York to Los Angeles are transported as follows: The call is sent first to either Chicago

$3Be$

or Memphis, then routed through either Denver or Dallas, and finally sent to Los Angeles. The number of phone lines joining each pair of cities is shown in Table $39.$

a Formulate an LP that can be used to determine the maximum number of calls that can be sent from New York to Los Angeles at any given time.

b Use the Ford$-$Fulkerson method to determine the maximum number of calls that can be sent from New York to Los Angeles at any given time.