my answer: 6

how i solved:

eigenvalues of adj(A) = |A| / eigenvalues of A = -8/2 and -8/-4 = -4 and 2. hence, x = 2, y = 4. so, x + y = 6.

however, answer key: -6

how i solved:

eigenvalues of adj(A) = |A| / eigenvalues of A = -8/2 and -8/-4 = -4 and 2. hence, x = 2, y = 4. so, x + y = 6.

however, answer key: -6