a) Suppose that B and C are invertible 4 x 4 matrices satisfying the following: . Columns 1 and 2 of B- are, respectively, and . Rows 3 and 4 of C-1 are, respectively, [0 -2 0 1] and [1 1 -1 -1]. If X = BC, find the (3, 1)-entry of X- and the (2, 4)-entry of (XT) -1. Explain your answers fully. (b) Let A and B be n x n matrices, and let y be a non-zero vector in R". Show that if A - B is invertible, then the equations Ax = y and Bx =y do not have a common solution x E R". Hint: Suppose that X is some solution to both equations, and aim for a contradiction