Consider the following
$$\max 3x_1+x_2\\ s.t. -x_1+2x_2\le0\\ x_2\le4$$
a) Sketch the feasible region
b)Verify that the problem has an unbounded optimal solution value
Attempt:
a) (Here the region looks bounded but it's unbounded, sorry I don't know how to use Mathematica very well..) 
b) I tried to use the simplex algorithm but when taking the pivot column which was $[-1\ 0\ -3]^T$ and trying to divide by the other column (the last one of the tableu) $[0\ 4\ 0]^T$ I got $\frac{0}{-1}$ ,4/0,$\frac{0}{-3}$, I got a division by $0$.
What can I do here?
How can I do b) with this?
Could someone help me please?