Solution:
we have been asked to Explain how comparing 645 and 738 is different from comparing 645 and 649.
There is one point that---in both the case 645 is smaller one where as the other number of the pair is bigger one.
Specifically the difference between 645 and 738 is

And the difference between 645 and 649 is

Hence the difference of first pair is larger than the difference of second pair.