Answer:
Thus he was able to save 4.438 dollars by paying 30 days before due.
Explanation:
given that Mr. Davis borrowed $600 for 60 days at 9% annual interest.
Thus interest payable for 60 days =

Because he paid fully after 30 days his interest would have been only for 60 days
or half of interest for 60 days
So savings of interest = 50% of 8.876
=4.438 dollars
Thus he was able to save 4.438 dollars by paying 30 days before due.