Hello, there was a matrix problem I was unable to work out completely:

'Your task is to crack the following code and find the encrypted word.

To make your task easier, the following information about the encoding matrix is given:

Position 1,1 in the encoding matrix is an even number

The decoding matrix only contains integers

Position 1,1 in the encoding matrix is the negative of the number in position 1,1 in the decoding matrix

Modulo arithmetic hasn't been used

My coded message is:

91, -38, 137, -59, 145, -59

How would I go about solving it; I know that E^-1 x EA will decipher the message. But would I place it in a 2x2 or a 3x3 matrix? How would I work out the encoding matrix? Thank you in advance!