solving equations in multiple variables with Transfer Matrix Method

Hello there!

I do have a problem with this calculation.

The original code looks like this:

clear all
format long
N = 6;
% syms A B
A = [];
B = [];
for kk=1:N
  A = [A sym(['A' num2str(kk)])];
  B = [B sym(['B' num2str(kk)])];
end
M = [1,2;3,4];
A(N) = 0;
B(1) = 0;
for ii = 1:N-1    
  fab = M*[A(ii+1);B(ii+1)];
  fa(ii) = A(ii)-fab(1,1);
  fb(ii) = B(ii)-fab(2,1);    
end
s=solve(fa,fb);

but these B matrices cannot be calculated. I hope someone can give me a good advise, how to deal with that. Thank you!