See image. a) and b) have been solved. The problem is c)
The Attempt at a Solution
I really have no idea where to begin. For the three systems given there are solutions x in range(A) for system 1 and 2 but not for 3. Therefore I have been trying to spot some obvious difference between system matrix A of system 2 and 3 but I cannot think of any clearly different property that could be linked to b.
Any hint just to get me started would be much appreciated.