6 1/3 and 2 1/3 are mixed numbers because they are a combination of a whole number and a fraction. They could be represented like:
6 1/3 = 6 + 1/3
2 1/3 = 2 + 1/3
To substact them, we need to convert the integer into a fraction. Since 6 = 6/1, we can multiply the numerator a denominator by 3 to get an equivalent fraction. We will do the same with 2 1/3.