i need help

if

$\displaystyle

A=\begin{pmatrix}1&0&2\\0&1&0\\2&0&1\end{pmatrix}.

$

calculate B3-3B2-B+3I

the B3 and the 3B2 the 3 and the 2 are above but i dont know how to type them here

please help how im gonna calculate B if i only know A?

pls answer me someone