A message was encoded using the matrix

Question

[7 2
3 1]
and you can decode the message 2 numbers at a time in a [1 x 2] matrix.

Here are the first four numbers:

66 21 119 35

I know it's coded row matrix times the decoder = the uncoded row matrix. (The key is A=1, B=2, etc.) I'm just not sure how to, because i tried it and got really large numbers. Help please?

thank you!

Answer 1

you will need the inverse matrix of
7 2
3 1 which is

1 -2
-3 7