One, two people should go this way. A It takes 30 minutes to walk and 20 minutes to walk. After walking for 3 minutes, A found that she didn't take anything, which delayed for 3 minutes. I walked for a few minutes before I saw him.

Solution: A is 3+3+3=9 minutes later than B.

Think of the whole distance as 1.

Then the speed of a = 1/30.

Speed B = 1/20

When Party A packed up and set out, Party B had already left 1/20×9=9/20.

Then the distance between Party A and Party B is1-9/20 =11/20.

The sum of the speeds of Party A and Party B =1/20+1/30 =112.

Then meet again in (11/20)/(112) = 6.6 minutes.

for reference only