A =. Multiply the third column of the matrix A by 2 and add it to the second column. You will get the matrix B then B = . The basic property of the determinant is that under such transformations of the matrix, determinant remains the same: det(B) = det(A). Now determinant B is easier to calculate than determinant A. Omitting the zero terms, det(B) = (-7)*(-5)*(-2) - 3*(-5)*(-1) - (-7)*(-8)*(-1) = -29. ANSWER