Judging by the question I noticed first that 6/9 is not quite simplified yet.
The first step I would take is to divide 6/9 by the GCF of the numerator and denominator, being 3. The fraction you should have from the result should be 2/3, which is equivalent to the other 2/3 fraction.
Thus 6/9 is equal to 2/3 if simplified by diving the fractions numerator and denominator by 3.
