Here is the sentence again:

As her teachers had recommended, Madison tried to study in the library but discovered that the good music, unlimited soda, and big tables at the campus café made a great place to do homework during fall semester, Madison must have eaten 150 pizza slices while she slogged through Fundamentals of Biology.

The blank space between homework and during makes a fused sentence. At this spot, there are two complete sentences joined with no punctuation, causing a major error. Madison tried to study in the library ... begins one complete sentence. During fall semester, Madison must have eaten 150 pizza slices ... begins the next complete sentence.

To fix this problem, you could put a period after homework and capitalize the D for during.

Go to the next sentence.

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