Take another look at the sentence:

When Javier was supposed to be in trigonometry, he was instead flirting with pretty girls in the cafeteria needless to say, he was inadequately prepared to make the 98 that he needed on the final exam to pass the course.

When Javier was supposed to be in trigonometry is a subordinate clause, which cannot stand alone as a complete sentence. He was instead flirting with pretty girls ... is a main clause. When a subordinate clause introduces a main clause, you should use a comma between the two.

Go back to the sentence to try again.

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