I want to decrypt an Affine cypher.
Definition: a^-1(c-b)
a = 5, b = 13
Range: Alphabet (26 letters) Letter to decrypt: K (c = 10)
So: = 5^-1(10-13) = 5^-1(-3)
I am not sure what do to next.
My approach: 1.) 5^-1 mod 26 = 25 => 25(-3) = 75 mod 26 = 23?
2.) = 5^-1 (-3) = -15^-1 = -15 mod 26 = 1?
But the result should be 15!