@amiablehummingbird Good question!
So, both buckets are being filled up at the same rate. But, since the 4-pound bucket holds less, it's going to dump more often than the 7-pound bucket. How much more often? Well, since the 4-pound bucket is \(\frac47\) of the size of the 7-pound, it's going to have to dump \(\frac74\) as often in order to take the same amount of corn.
Thus, since it dumps \(\frac74\) more often, \(\frac74\cdot112\) is the answer.
Let me know if this makes sense!