(a) Write down a 4×4 elementary matrix that replaces row 3 with ( row 3+8 row 4). Write down the inverse of this elementary matrix. (b) Write down a 4×4 elementary matrix that interchanges row 1 with row 2 . Write down the inverse of this elementary matrix. (c) Write down a 4×4 elementary matrix that scales row 2 by −3. Write down the inverse of this elementary matrix.