Need help with creating an if/then/or formula

Can you provide any sample data? Dropdown is pretty easy, but where do we get number of students from?

have you created a spreadsheet - you can load here?
with a layout you want

you can use a lookup formula or hardcode and IF/lookup formula

But we need to see the layout to really advise

whats the max number in the class

Also is that $15 per student for 3 = $45 then 4 = $65, 5 = 85
1 = 15
2 = 15
3 = 15
4 =20
5 = 20
6 =20
etc


Please upload a sample of your workbook to the forum, Make sure you have removed any private information, remember this is a public forum and so available to anyone
Would like to see an example of your data and also a manual mock up of the expected results you want to achieve.

To attach a file to your post,
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Try the attached. To add a new class, just start typing in the next available row.

Formula:

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I think you want this to be

Formula:

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Also look at my file to see how the one for vets is treated differently since that's a flat rate.