Let A be a 3x3 real matrix. Suppose 1 and -1 are two of the three Eigen values of A and 18 is one of the Eigen values of $A^2 + 3A$. Then.
a) Both A and $A^2 + 3A$ are invertible
b) $A^2 + 3A$ is invertible but A is not
c) A is invertible but $A^2 + 3A$ is not
d) Both A and $A^2 + 3A$ are not invertible