First let's round the numbers 6 2/3 and 2 14/15.
2/3 is approximately 0.66, so it's closer to 0.5 than 1, so let's round the mixed number to 6 1/2.
In the same way, we can round 2 14/15 to 3, because it's closer to 3 than to 2.5.
So the final calculation is:
Now, calculating the difference without approximation, we have: