Consider the following tableau corresponding to a basic solution of a maximization LB with original non-negative variable X1, X2, X3 and slack/surplus variables X4, X5, X6: Z X X X3 X4 X X6 RHS Z 1 0 -5.5 3 0 0 7.5 48 X4 0 0 -1 1 0 1 10 X5 0 0 -1 1 0 1 -1 5 X1 0 1 3 -1 0 0 1 6 12 (1) Assuming X2 is selected to enter the basis, if X4 is selected to exit the basis based on the minimum ratio test, the value of tableau entry & 12 must be at least