That would be 23/6 which could also be written as 3 5/6 when written as a mixed number
You would subtract the denominators just as you would in any normal subtraction problem (56-33) and you keep the denominator the same. To write is as a mixed number you would see how many times 6 can go into 23 evenly, which would be three, and then the remainder would be the numerator. 3 5/6