A firm has prepared the following binary integer program to evaluate a number of potential new capital projects. The firm's goal is to maximize the net present value of their decision while not spending more than their currently available capital.

Max 100x1 + 120x2 + 90x3 + 135x4

s.t.

150x1 + 200x2 + 225x3 + 175x4 500 {Constraint 1}

x1 + x2 + x3 + x4 2 {Constraint 2}

x2 + x4 1 {Constraint 3}

x2 + x3 1 {Constraint 4}

x1 = x4 {Constraint 5}