(a) Find all solutions $X=\left(\begin{array}{cc}x & y \\ z & w\end{array}\right)$ to the matrix equation $A X=X B$ when $A=\left(\begin{array}{rr}1 & 2 \\ -1 & 0\end{array}\right)$ and $B=\left(\begin{array}{ll}0 & 1 \\ 3 & 0\end{array}\right)$. (b) Can you find a pair of nonzero matrices $A \neq B$ such that the matrix equation $A X=X B$ has a nonzero solution $X \neq \mathrm{O}$ ?