Take another look at the sentence:
Crossing his arms and closing his eyes, Pedro's book bag was zipped close,
even though his math professor continued solving problems at the board.
Crossing his arms and closing his eyes, a participle phrase, comes right before book bag, an illogical target. [Pedro's, a possessive noun, functions as an adjective describing book bag.] People, not book bags, have arms and eyes! If book bags had appendages and sight, that would just be creepy! Before you continue, review the rules for misplaced and dangling modifiers.
Go back to the sentence to try again.