it is already in simplest form
12/35
you cannot divide top and bottom by any same number evenly
12 over 28 in simplest form is 3 over 7.
21/36 in simplest form is 7/12
12/5 as an improper fraction is already its simplest form
18 over 12 in a mixed number in simplest form is 11/2 or 1.5
1/4
3/4
1/2
12/5
1/12
12/77 is already in simplest form, since the greatest common factor of 12 and 77 is 1.
12/15 = 4/5
12/4 = 3/1 = 3.