5. Suppose A is a 3 x 2 matrix and that R is the reduced row-echelon form of A. Suppose that A and R are related by the following sequence of elementary row-operations: R2%R1 razed?3 R23R1 %Rl A )))) R (a) (4 points) Write down the four elementary matrices corresponding to the four ele mentary row operations displayed above. (b) (1 point) Find an invertible matrix M such that A = M-'R.2 2 4 (c) (5 points) Let B = [ 1 1 2 ]. Assuming that the matrix equation AX = B has no 6 6 12 solutions, prove that A must be the zero matrix