Consider the following three linear programming problems in two variables that illustrate various special cases. By means of the graphical solution method , indicate which is infeasible, which has unbounded solutions, and which has multiple optimal solutions?.
a. Max X1+X2 subjet to : X1+X2 ≥ 400; -X1+2X2 ≤400; X1, X2≥0
b. Max 45X1 + 300X2 subject to: X1 + X2 ≤ 200
9X1+6X2 ≤1,566; 12X1+16X2 ≤ 2880; x1, x2 ≥ 0
c. Max 7X1+5X2 subject to: 4X1 + 5X2 ≤20; 5X1+4X2≥28; X1+X2≥ 0