@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!