The answer would be 7/3. You would divide them both by 3. You just divide them by the same number to the point were you cant divide both by the same number anymore. For example 18/9 you can divide it by 2 to get 2.
Its 2 1/3
9 goes in 21 twice and theres 3 left over
2 3/9= 2 1/3
