39 people : 12 days : 5 hours
//Find 1 person
1 person : 12 x 39 days : 5 hours
1 person : 468 days : 5 hours
//Find 30 people:
30 people : 468 ÷ 30 days : 5 hours
30 people : 15.6 days : 5 hours
//Find 1 hour:
30 people : 15.6 x 5 days : 1 hour
30 people : 78 days : 1 hour
//Find 6 hours:
30 people : 78 ÷ 6 days : 6 hours
30 people : 13 days : 6 hours
Answer: 13 days
