3. A milling machine is assigned to process three jobs. Both processing time, due date (in days), and penalty cost of delay for each job are given in the table below. The due dates are measured from day 0, the start time for processing the first job. Processing time (day) Job 1 2 Due date (day) 25 5 20 3 15 Formulate this problem as an integer programming model to determine the job sequence that minimizes the late penalty cost for processing all three jobs. Define decision variables, objective function and constraints clearly. Zmax 21 x + 11 X s.t. 22 36 Late penalty ($/day) 10 30 20 4. Solve the following pure integer programming problem by branch and bound (B&B) algorithm: 7 x + 4 x2 + x3 = 13 X1, X2, X3 are non-negative integers