QUESTION 39. The linear programming model for this problem should be

QUESTION 40.

The restrictions X SUBSCRIPT 1 COMMA X SUBSCRIPT 2 GREATER OR EQUAL THAN 0 and T SUBSCRIPT 12, T SUBSCRIPT 13, T SUBSCRIPT 21, T SUBSCRIPT 23, T SUBSCRIPT, 32 GREATER OR EQUAL THAN 0 in the model means

	Each decision variable must be positive in the optimal solution.
		Each decision variable must be nonnegative in the optimal solution.
		All of the above.
		None of the above.

O max 11x + 13x +t12 +13 +22+123 +132 s.t. 2.5x +2.2x +t12 +13 -21 1.8x +1.4x -t12 0.9x1 +1.2x -t13 t12 +13 1200 +t21 +t23 -132 1000 -t23 +132S 560