Brought two workers. It is emphasized here that the explorers brought their own food. There will be 3x4= 12 days of grain when we go.

Day 1 day: 12-3=9 (day) is left. It takes 9- 1=8 (day) to give a worker a day's food.

The next day: there are 8-2=6 (days) left to take back to the workers. 6-2=4 (days)

Day 3: 4- 1=3 (days)

Day 4: 3- 1=2 (days)

Day 5: 2- 1= 1 (days)

Day 6: 1

It's done!

I'm a teacher. You can come to my QQ group to chat when you are free: 543 13657.