A linear programming model is given as follows: Minimize = 81 + 62 Subject to 41 + 22 20 61 + 42 12 1 + 2 6 1, 2 0 (Solve by geometric method, do not use Excel Solver) (a) Define the feasible solution area and obtain the optimal solution graphically (b) If the coefficient of 2 in the objective function decreases to 4, what effect will be? (c) If the second constraint, 61 + 42 12, is removed from the given model, what effect will be? (d) If a new constraint, 41 + 62 24, is added to the given model, what effect will be