Let x = the hourly traffic down Rush St..,
let y = the hourly traffic down Pledge Ave.,
let z = the hourly traffic down Fasttrack Ave.,
let w = the hourly traffic down Depledge Blvd.,

If we set traffic in = traffic out at each intersection, we get the following system of equations

x + z - w = 100
x-y = 25
y + z - w = 75

and the general solution is:

x = 100 - z + w
y = 75 - z + w
z, w arbitrary (and non-negative).

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