The Affine cipher is a monoalphabetic substitution cipher and it can be
the exact same as a standard Caesarian shift when
"a" is 1. Mathematically, it is represented as `e(x) = (ax + b) mod
m`. Decryption is a slightly different formula, `d(x) =
a`^{-1}(x - b) mod m.

To encode something, you need to pick the "a" and it must be coprime with
the length of the alphabet. To make this easier, I have the (+) and (-)
buttons to change the A to the next higher or lower coprime number.

This is your encoded or decoded text: