Consider the affine enciphering transformation:
f(x) = 9x + 4 mod 49
on single letter message blocks of the ordinary English alphabet A - Z
and the letter b for “space”.
How many more letters can we add to our alphabet without any
further changes to our encoding procedure?
Would this just be 26 x 2 = 52
52 - 49 = 3, hence 3 more letters could be added?
Thanks in advance!