Real Eigenvalues question

Let A be a 4x4 matrix such that A^2-3A+2I=0 which two real numbers could possible be eigenvalues of A?

I realize that this is a square matrix, but I have no idea how to go at this problem ... Would I assume that the determinate of A matrix is the sum of the diagonals, or just use the quadratic equation and solve it. Its just the I matrix that is throwing me off.

Solving for t from t^2 - 3t + 2 = 0 yields t = -2, -1, the (double) eigenvalues for A.
(The polynomial given is the minimal polynomial for A, as its roots are distinct.)

I hope this helps!