Get the next date of a task related to an opportunity

I have two related tables, Opportunities and Tasks.  An opportunity can have many tasks.

I am trying to add a field on to my opportunity table to show when my next task date is and if there is nothing assigned to shade the opportunity yellow to signal we are not doing anything with it and we need to create opportunities....

I have a summary field for the number of tasks so I can easily shade the record yellow if the number of active tasks = 0

How do I go about getting the next task date?  I was thinking to use a summary field with a min of task due date but that doesnt appear in my opportunity table.

Thanks!

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Ivan Weiss
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