$Ifwe$ use the Hill cipher with $m=3,26$ English letters

and $10$ decimal digits $to$ encrypt plaintext "Engineer$1"$

$by$ using the key matrix $,$

$\left[\begin{array}{ccc}1& 2& 12\\ 8& 5& 6\\ 9& 3& 5\end{array}\right]$

then the obtained cipher text $is.(Note$ that $Z=25,$

$0=26,1=27,2=28.$dots. $.$ Hint: Use modular

arithmetic$)$