Let the rows of the given matrix be E1, E2 and E3, counting from the top to the bottom. Notice that the row 2E1 - E2 is equal to [-9, -2, -11]. It will be exactly equal to the third row, E3, if -9 = -6+k, i.e. k= -3. Then the determinant of the matrix will be zero. ANSWER. k = -3.