You have already figured out that having mixed levels of aggregation in your data is not the best way to go - but you can make it work in one of 2 ways - in Tableau
but you are going to need to think through the aggregation process for each calculations - for those that are you plan to aggregate to the "Catered amount spent" level you will have to Sum() the data - then compare it to an avg() or a min() for the catered amount spent -
if you use Tableau Prep you could bring your disaggregated data in as a file and aggregate the data to the higher level then bring in you "Catered amount spent" data and create the Join after the aggregation
Good luck -
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