You can
put this solution on YOUR website!Let him start out with

amount of rice
At the first he gives up 1/3 of his rice, so he has

left
At the second he is allowed to keep 1/3 of what is left,
so now he has

left
At the third, he gives up 1/4 of what remains, so he gets to keep
3/4 of what remains. Now he has

After passing through all three customs stations, he has 6 pounds less than he started with, so he has

multiply both sides by

He had 7.2 pounds when he started
check:

OK