Consider the following linear program: Max z= 2r1 + 4r2 + 4r3- 3z4 8.t. Di + *2 + I3 = 4 2+ 4x2 + 24 = 8 21, 22, L3, E4 2 0 (a) Write the associated dual problem. (b) Verify that XB = (x2, 23)" is optimal by computing 2, - e, for all nonbasic (c) Find the associated optimal dual solution from the appropriate z, -c, computed in part (b).