"Grey Out" options based on 1st option chosen

Hello,

I'm designing a form where an account manager can request a discount for their client.  What I DON'T want is them to be able to select multiple discounts.  I have the fields and table set as follows:

Fields (Checkbox format)
30%
40%
50%
80%

I want the form to work that once they select a discount (any) it will grey out ALL the others and if they want to select a different one, they need to Un-check the one currently selected first.

I was trying to use dynamic rules and it seemed to work for the first entry but then I got a message saying 1 rule would overwrite another when I tried to add a 2nd rule.  The rule I set which threw the error was:

When 30% is checked, make 40%, 50%, and 80% read-only
(This one worked great)

I get the error when I try to add:
When 40% is checked, make 30%, 50%, and 80% read-only.

I hope I'm explaining correctly, I attached a screenshot for clarification.  Any help you can provide would be great.

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Marshall Azar
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