You have to find the greatest common factor between them which would be 3 (to find the greatest common factor just write a list of the numbers that evenly go into the number your trying to find the factor of, and the largest factor the two numbers share is your greatest common factor) You then divide each number by your greatest common factor of 3 and you get the result 31/40.
So 31/40 is the simplified fraction of 93/120