3420/9=380 He used 380 boxes in his first week.
Answer:
36
Step-by-step explanation:
Multiples of 4: 4, 8, 12, 16, 24, 28, 32, 36
Multiples of 6: 6, 12, 24, 30, 36
Multiples of 9: 9, 18, 27, 36