if u have 1 number repeating, like 0.1111, then u put that 1 number over 9.....so it would be 1/9
if u have 2 numbers repeating, like 0.2323....then u put ur 2 numbers over 99.....so it would be 23/99
if u have 3 numbers repeating, like 0.324324...then u put ur 3 numbers over 999...so it would be 324/999.
now for ur problem.....12.1.....u have 1 number repeating...so put that 1 number over 9.......and dont forget ur whole number 12....so ur fractions would be : 12 1/9 or 109/9 <==