Dirk,
Did you test Dan's solution? It should work without the ranges due to the order in which the program runs its evaluations, i.e. - Will check <=3 first, if that fails will move to <=24, if that fails will just charge monthly rate.
TL;DR
But, with that being said, you can use AND to enforce ranges, but you have to declare the object you are comparing values to each time.
You have:
...
[Rental Days] >=1 AND <= 3, [Rental Item - Daily Rate],
...
You need:
...
[Rental Days] >=1 AND [Rental Days] <= 3, [Rental Item - Daily Rate],
...
for that to work.
However; I urge you to be careful with specific ranges. If you do not consider all possibilities your code will break.
For instance, your solution (with the AND operator) doesn't consider anything less than half a day (or a value between 0.5 and 1), or 3.5 days, or if someone submits the form without any days (blank), your code will break and the rate will not be set. Maybe this breaks nothing, maybe everything. Just be aware.
Hope this helps sheds some light.
~Rob
