He then went to see the oranges being harvested. He found out that they harvest 74 sacks per day and discard 71 of them. How many sacks of oranges will they have after 51 days of harvest?
Let's say that <code>s</code> is the number of sacks of oranges harvested per day. Then <code>d</code> is the number of sacks of oranges discarded per day. 

The number of sacks of oranges harvested after <code>n</code> days is <code>s * n</code>. 
The number of sacks of oranges discarded after <code>n</code> days is <code>d * n</code>. 

The number of sacks of oranges remaining after <code>n</code> days is <code>s * n - d * n</code>. 

Now, we know that <code>s = 74</code> and <code>d = 71</code>. 

The number of sacks of oranges remaining after <code>51</code> days is <code>74 * 51 - 71 * 51</code>. 

Therefore, the answer is <code>74 * 51 - 71 * 51 = 2323</code>. 