i have hill cipher

AR3TSBXS0KY8C6L1EXC0TDJMLUDR5KVGISGEWFU... WB44GJE11O76VLSPKAQG9APM-4?ZTCCKN3KJPJF.... 991N06SHLKVK97RC3Y?


can someone tell me the key.

known plaintxt is

DEAR AGENT BOB

CODEWORD

also charecter set is " ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789.?,-...

Note there is space in Char set before A