He then went to see the oranges being harvested. He found out that they harvest 76 sacks per day and discard 64 of them. How many oranges do they harvest per day if each sack contains 50 oranges?
: 

1. He sees the oranges being harvested. This means that the oranges are being collected into sacks. 
2. He is told that they harvest 76 sacks per day. This means that they are collecting 76 * 50 = 3800 oranges per day. 
3. He is told that they discard 64 of the sacks. This means that they are discarding 64 * 50 = 3200 oranges per day. 

Therefore, the total number of oranges they harvest per day is 3800 + 3200 = 7000 oranges per day.