How to save and crossing process of multiple sequence file?

suppose I have two files (attached). I plan to do cross math operation, for instance: the first column of A file multiply with the third column of B file.How to do that? Here the script I used (in this script, I can only process different column of the same file).

    for i = 1:2
    id = i;
    str_id = num2str(id,'%4.1i');
    ts = load(['old_',str_id,'.txt']);
    x=ts(:,1)
    y=ts(:,2)
    z=ts(:,3)+ts(:,2)
    b = [x y z] 
  end

save('new_',num2str(i),'.txt','b','-ascii')

Then, when I try to save it as new sequence file, it only saves the last file (new_2). Thank you for your help