A group of students is preparing for a bake sale to raise funds for their school library. There are 3 classes, with each class consisting of 20 students. Each student bakes 12 cookies per day for 4 days. If they package the cookies into boxes, each containing 10 cookies, how many boxes of cookies can they sell at the bake sale? Let's think step by step and output the final answer within \boxed{}.
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