Depending on how exact your teachers want you to be; The closest amount of Centimeters in a 12 inches is 30.48. In fractions there are no decimals unless you work infinitely until they are cast out of the fraction.
6 is a fifth of 30. Being how 30.48 cant be rounded to 30.5 we round to 30. 6 centimeters is approximately 1/5 of a foot. 30÷6=5 6×5=30