Linear Algebra Eigenvalue

Is λ = -3 an eigenvalue of [-1 4 ; 6 9]? Why or why not?

Thanks!

| -1+3 4 ; 6 9+3 | = (-1+3)(9+3) - (6*4) = 30 != 0. Therefore -3 is not an eigenvalue.


[Ed. What a mistake. (-1+3)(9+3) - (6*4) should be 0. Ian's answer is right. ]

Actually (-1+3)(9+3) - (6*4) = 0. Therefore -3 is an eigenvalue.