So one day, this kid and his friend are in line at the school cafeteria. The kid looks at the menu and sees that today's lunch is $5; he looks in his wallet and sees he has only $3.
Distressed, he turns to his friend and queries, "I don't have enough money to get lunch today! What do I do?"
And his friend replies, "2x + 5!"
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Don't get it? )