I don't know if I've posted this in the right place but I thought I'd give it a go anyway.
For question see attachment below.
So for part a) max z:150X11+350X12+300X13+100X21+500X22+400X23
For (b) eliminate first constraint and label constraints: u2,v1,v2,v3
Then solve for us and vs and i get u1=0 u2=100 v1=0 v2=400 and v3=300
Then c*12=50 so not optimal
(c) Enter X12 into basis create loop etc. but that give new solution as X12=40, X21=30 and X23=60. But then when you go through us and vs again to test for optimality, you've got 5 variables to solve for and only four equations so I'm stuck. Help please!