He then went to see the oranges being harvested. He found out that they harvest 8 sacks per day. How many days will it take to harvest 24 sacks of oranges?
Let's say that x is the number of days it takes to harvest 24 sacks of oranges. 

We know that: 

8 sacks per day * x days = 24 sacks

8x = 24

x = 3

It will take 3 days to harvest 24 sacks of oranges.