Well, since this has been up for a few days, and nobody else is helping, I thought I'd pitch in and add my thoughts.. I can't help with part (b), since I'm unfamiliar with the "Inversion Algorithm". However, part (c) is pretty straight forward.

Use the same method for finding the determinant that you used in part (a), except this time, replace element

(the two in the upper-left corner) with a 1. You'll find that the determinant is zero. A determinant of zero means that the matrix is "singular", and therefore has no inverse. I'm sure you understand (or can figure out) why that is.