EXERCISES Consider the following linear programming problem. maximize z = 4x, + 3x2 subject to -x1 + x2 = 6 2x, + x2 = 20 x1 + x2 = 12 X1, X2 20 (a) Solve this problem graphically. (b) Solve this problem by the algebraic simplex method described in Example 4.1, and at each iteration, identify the corresponding extreme-point solution on the graph. (c) Identify the basic variables, the nonbasic variables, and the basis matrix B at each iteration