I see.
This si a bit tricky as what you want are those that have BOTH 7000 and 2450 as values.
Here's one way:
Group by the accident.
Report->Edit Selection Formula->Record:
{table.offense_code} in ["7000","2450"]
Now create a formula to count the number of distinct offense codes per Accident:
distinctcount({table.offense_code},{table.accident})
Now in the Report->Edit Selection formula->Group place:
distinctcount({table.offense_code},{table.accident}) > 1
That should work.
-k