Well, darling, 28 in simplest form is just 28. Can't simplify it any further unless you want to start getting into fractions or decimals. But why complicate things when you can just enjoy the simplicity of good old 28?
28/55 is in its simplest form.
28/9 is in its simplest form.
28/185 is in its simplest form.
69/28 is in its simplest form.
13/28 is in its simplest form.
9/28 is in its simplest form.
33/28 is in its simplest form.
11/28 is the simplest form.
9/28 is in its simplest form.
43/28 is in its simplest form.
The simplest form of the fraction 13/28 is 13/28. This number cannot simplified any further.
28/25 is in its simplest form.