It worked for me tho I found it unfair for user with 20 and 10 days rental get equal fee reduction of $50. It would be good if the (amount to be decreased for both 3 and 7 or more days) is dependent on the multiples of the days. This would make user with 20 days get twice reduction than 10 and the same goes to 3 days discount.
And for those who are wondering how to discount for higher numbers with both 3 and 7 days discounts, it would be simpler if the higher discount among the two (refering to 3 or 7 days) would be chosen.
JUST A SUGGESTION... * _ * + _ + * _ *