Table: 2002 fivb women 's volleyball world championship qualification
Question: What was the average score difference in the matches that ended with a 3-0 score? 
Step 1 (Operation, Grouping): score
Step 2 (Operation, Indexing): total
Step 3 (Reasoning, Grounding): score difference, total difference
Step 4 (Reasoning, Aggregating): AVG, total difference
Answer: 29