Keep it simple... Set the value to 1 if it meets the criteria or 0 if not.
Then simply let the aggregation handle the math.
Create a Query Item, "7 or better":
IF ([package]..[data-item]>=7) THEN (1) ELSE (0)
Then to get your ratio, divide the count of the rows by this query item.
This of course will not make much sense in a detail report, but in a summarized report (where there is some level of grouping and therefore, some aggregation) it will get you your result.