Luca went to a sandwich shop for lunch. The sandwich he bought was normally $8, but he had a coupon for a quarter of the price off. He then upgraded it with sliced avocado for an extra dollar. After adding a drink and a $3 salad, his total lunch bill was $12. How many dollars did Luca pay for his drink?
Please reason step by step, and put your final answer within \boxed{}.
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