Review the item:
With regret, Jack slung the heavy backpack over his shoulders and fleed the cold library. If he had brought a jacket, he could have continued fantasizing about the cute librarian at the reference desk.

The second verb, fleed, is the problem. The sentence requires the simple past. Fled is the correctly spelled form.

Verb Simple
Present
Simple
Past
Past
Participle
flee flee(s) fled fled

Had brought, the verb you chose, is perfectly correct. Before you continue, review the rules for irregular verbs.

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